I liked the way they made each zone makes sense internally, with HFC being the best example of this. Quest givers lead from node to node, and back again. It was a massive, massive step up from Azeroth. That said, on a pvp server, it never felt like pvp was going on. There was (thankfully, but sadly) no "I survived Stranglethorn Vale" experience.

The quest rewards made more sense, but, I gather left some classes unhappy. But then again, getting rid of strength/agility cloth quest rewards shouldn't be applauded. Rather, expected.

My mine gripe with BC is the art direction. It was awful. The original wow was really interesting because you were inside warcraft. The zones were different, and well designed (from a graphical point). Desolace stands out for me, purely because going there depressed people. What more perfect emotion could a desolate wasteland inspire.

BC, on the other hand, was the weird space crystal thing. It worked in HFP. Was totally abandoned in Nagrand (which is one of the reasons the zone is so favoured, I think). But everywhere else just ratcheted up the ugly. The gear was ugly. The weapons were ugly. Draenai are ugly. I think it's no coincidence that people still yearn after their Tier 2 gear. (Looks wise, at least).

The "let's make everything neon" philosophy gave us the "city" of Shattrath - and it's no coincidence that the only interesting parts of that city are the muddy, dirty, refugee camps.

As for people's comments about 5 mans being too short, or too long. Um, I don't know. When I first him outlands and did Ramparts and BF, I war really enthused by the pared down, trash lite feel of them. Maybe I was burnt out from running Scholo and UBRS for a year and a half, but the speed appealed to me.

Yet here I am now, after the brewfest boss, and wandering through old instances for the Scourge invasion bosses, thinking: these were real instances. We didn't need a rep grind to come back in here, because there was so much to do. So much loot. And so much of it in stages, that you had reasons to come back. Nevermind that a burning Stratholme will always be more interesting to look at than another purple eye-sore.

The raids were okay - I really like Kara, though I understand that it was probably too difficult for a starter encounter. Plus, of course, really making putting together your first 25 man difficult. I kinda wish there were more stand-alone bosses.

Oh, and one of the big things I think everyone is missing that should go on the Blizzard "gold star" list, is the reduced potion requirements for raids. Man that was painful.

The length of 5 man is about right for semi-competent people in TBC. For people that needed to look for pugs, the amount of time spent in the instance plus the time needed to find a group was simply rather annoying and long. This is probably why Blizzard is tuning the 5 man instances in WoTLK to be even shorter and easier, at least at the moment. Sure, it allows the over-geared and the better player to blow through the instances in record-setting time (and most hardcore players will probably level like this on Wrath release to get away from the lag hell that is going to be known as Borean Tundra or Howling Fjord, or farm badges at a very fast pace), but for a typical player that has about 10 hours of playtime a week, this allows them to progress themselves in 5 mans at a much more comfortable pace.

I'm still not very optimistic about raiding in WoTLK, but that has nothing to do with class balance, but rather that this is a very matured game already. I sincerely doubt that they will be able to come up with very original concepts to make fights interesting and challenging. TBC was already significantly easier than classic raiding because of the fact that a lot of concepts were recycled in TBC, just forcefully made harder in terms of numbers (healing, dps, tank dmg, etc). Now with raid stacking almost eliminated by greatly limiting cooldowns on enhancement abilities as Bloodlust/Heroism, potions, and stones, the amount of variance a raid can change by bringing different classes becomes extremely limited, which allows for more proper tuning.

Edit: To avoid confusion about the seeming contradiction I have with my previous post. What I mean about "raiding being too easy" is that the concepts are old, even in TBC. Raiding in early TBC is more tedious, if anything. Al'ar required a lot of execution, which was very refreshing until they changed it. Hydross had unreasonable crushing and high HP. Aside from those two, the fights weren't hard; they were just tedious to farm for with the 2 million consumables you use every night, which lead to the "1 hour of raiding, 3 hours of farming" type of jokes. In MMOs, things are very "hard" when you expand the timesink into an even bigger one for no good reason.

<snip>

Deleted. Sorry, I skipped Kaubel's request.

Zones and Quests
Much more efficient locations for quests : they were placed in "node", so you could take them all at the same time, and then go to business. More efficient, and many times quite logical, but in retrospect, it's also a bit damaging to immersion compared to the previous large pre-TBC zones where you could explore and discover an unknown quest-giver.
The zones were interesting and beautiful, at least at first (expect with Blade's Edge, which was quite boring). But somehow, they lacked the immersion of pre-TBC zones. The atmosphere was strong, but somehow I wasn't as drawn into it than in Westfall or Stranglethorn. Can't really put my fingher on what went wrong, but it definitely feels like there is a lack somewhere. Probably lore.
Daily quests are basically glorified farm. I don't really see what point they serve except alleviating farming on one hand while creating a vicious circle of farming required on the other.


5-men content
Definitely meh.
I hate the "tunnel" effect. Short, boring, follow-a-corridor-with-three-boss-chekpoint and completely devoid of personnality. TBC instances definitely lack the background and verisimilitude of the pre-TBC ones. They are too formatted to fir the same mold.
The heroic system was a great idea, but too many nerfs made it lose its very concept, and it became another boring farm.
The saving grace : mobs and bosses are much more varied/complex/interesting than pre-TBC ones, which were basically tank'n'spank with a special ability thrown here and here (if they had any at all).
The reputation system was annoying, but at least it gave you a reason to come back later, so once they lowered the heroic key to honoured, it became rather a good point.

But all in all, I won't remember fondly TBC 5-men, except for the CoT ones, which, not coincidentally, went a bit away from the simplistic design (though both had still the three "checkpoint bosses", but at least in a more creative way).


Raids
The change from 40 to 25 was great in my opinion. More game, less logistics.
Karazhan was the best instance in all WoW history, bar none : lots of lore, superb atmosphere, lots of boss, varied fights.
There was a lot of improvement in TBC raids compared to vanilla, but with a lot of hiccup on the road : it was basically shitty before 2.1 (insane flasks/elixirs costs, far too hardcore from the start, horrible gear progression...).
After 2.1, it was better, but still with good and bad mixed. The bad was, basically, that the instances weren't very interesting in themselves, the insane attunements, and lack of background in general. The good was interesting bosses and new raid dynamics : much more spec were raid-viables, which was a welcome change from pre-TBC, with a single spec (healing) for all "hybrids".
I also much prefer the token system to the infuriating and frustrating "random tier piece".


PvP
To be simple, I HATED with a passion the TBC PvP. Arena has severaly damage the whole game, taking a much too important places in balance and gearing, and it was probably the worst addition in the whole expansion.
In my opinion, PvP in TBC was simply a disaster.


Professions
I loved jewelcrafting. It was not a lot, but it was really fun. And it didn't require mind-numbing farming.
Many professions were too annoying to level with primal requirement bonanza, and not useful during leveling, as usual.
At least, they were all interesting for the special patches/thread/enchanting/slots they could produce, except for blacksmithing which was left in the dust once PvP gear offered as good weapons as they could craft - the "upgrading" idea was great, though.


Misc
Badges were initially an excellent idea, like arena. But, like arena, they took such a place that they damaged and depreciated the rest of the game. They were good at the role of "getting catch-up gear", but they spilled from this role and became "get your high-level free raiding epics".

FAR TOO MANY EPICS. Purple has completely lost its meaning. Too much gearing in general. The old pre-TBC instances offered usually green items. The largest bosses of the instances offered blues. Some extremely rare epic drops on the end bosses of high-end instances. ZG and AQ20 still offered largely blues, and some epics. In TBC, every guy and his mother drops truckload of epics, and you can get epics in one million and a half ways.
Giving things away too readily drops its value, and purple is really the "regular" color of gear. Sadly, it seems it's even worse in the expansion :-/


Best and Worst
TBC was too much "game mechanics" and too little "immersion and atmosphere". The instance layout was terrible, and I was rarely drawn in, and felt disconnected from most of what happened. Lore was pretty horrible (the whole Blood Elves in Horde, the whole spaceship delirium, please...), or at least horribly butchered.
The mechanics and metagame were quite interesting, though, and there was many improvement in many parts of the game.
Sadly, the prominence of arena and the frenzy epic loots availability, destroyed many part of the game (again in immersion/atmosphere, but also in progression and accomplishment feeling).

Edit : how could I forgot this ? I absolutely LOVED the flying mount. One of the highest fun-point in my whole WoW life.

Zones and Quests
I enjoyed leveling in BC. Pre BC, the questing system didn't really give you very good rewards (remember every item having spirit on it?). In Burning Crusade, there was a clear progression and just about every quest would give you an upgrade. Plus, there were way more than enough quests for each zone. You could sort of pick and choose where you wanted to go. In vanilla wow, it was more or less - go to the Barrens, then eventually STV, etc. The quests in general were more conducive to leveling as well. There were less of those stupid delivery quests that made you run all the way across the zone.

Daily quests were great. It gave every class, no matter what spec or professions, a way to generate income.

5-men content
I liked how the dungeons in general were shorter than the vanilla wow dungeons. Taking 2 hours to complete an instance is too long in my opinion, they should take 45 minutes, tops. I'd rather not get into the heroic badge gear debate because that degrades into Casual vs Hardcore. But I will say that from a raid leaders perspective, it's much nicer knowing that no matter what raiding experience an applicant had, they at least are going to have some T6 quality gear from heroic badges.

Heroic dungeons and later the Daily Heroic quest made every dungeon worth revisiting and somewhat entertaining.

Raids
I like how they expanded on the tokens for T6 system. I hope they stay with 3 set tokens per boss kill model. I enjoyed Black Temple and I enjoyed Sunwell Plateau. I hated Serpentshrine Cavern - the trash often felt harder than the bosses themselves. I think we can already see from wrath that they've learned that making entry level 25 man raids too difficult is a bad thing.

Another thing Blizzard needs to remember is that the loot from raids needs to be good. When BC was first released, SSC gear was often worse than blues from questing. This has long since been resolved, but as arena gear keeps getting better and better, they're treading on a thin line.

I don't think anyone thought the way they distributed Atiesh was a bad thing - why did blizzard go back to a RNG system for legendaries? Bad move. So frustrating for me personally when my guild killed Illidan 50 times since we first started doing BT and never got a mainhand warglaive, when one of the bottom of the barrel guilds on my server has two complete sets after killing Illidan 6 times.

Sunwell was great except for the stacking of Shaman. This has been pretty well documented in other threads, no need to QQ more.

PvP
I loved arena, but I hated druids. Arena was the main reason why I even bought the expansion in the first place. It was great until Druids started to dominate 2v2 and 3v3. Then it felt more to me like a battle to find the better druid partner. Most of the problems with S3 and S4 I think could have been solved simply by more players queing up (or just removing the Druid class from the game)- but once everyone got their rating they wanted they just played their 10 games a week and dodged any decent teams. Sadly, I don't think they'll ever get class balance perfect. Case and point - the last 3v3 tournaments before 3.0 was released were all won by Warrior Warlock Druid - and most of the finals matches were straight up mirrors.

Battlegrounds were just the same as vanilla wow. Making honor a currency used to buy pvp gear was obviously a great improvement over the High Warlord system. However, I hate the matchmaking system. It doesn't reward you for playing as a team, since the games take longer to pop up and you'll only play against another team - meaning less honor per hour than just solo queing. People resorted to using third party addons that cleverly made every player individually que at the same time to circumvent the matchmaking system. Even when I qued by myself, since my gear is better than the average player I'd wait in a long que, only to get into a game that's already started with 3 horde versus 15 alliance.

Professions
Giving every profession something unique to that profession only as well as giving them access to raid quality loot was a very good idea. It made professions actually matter.

On the other hand, Sunwell was so very well tuned that DPS had to be more or less perfect. With items like Drums of Battle in existence, it made it virtually a requirement for any decent guild to have everyone be leatherworking. The same can be said for when SSC and TK were new. Alchemy stacking was ridiculous - Flask, 4 different kind of elixir, food buffs, etc. Making more professions give you something useful for raid buffs is a good thing - but keep it in check. They need to be careful not to make one particular profession SO good that everyone MUST have it, like Tailoring pre-T6 content or Leatherworking once Sunwell was released.

Misc.

Mana. Mana was stupid in Burning Crusade. It got to the point where there was no point at all in keeping track of it in PVE, every class would never run out of it. This just led to dumb stuff like ignoring the intellect and MP5 stats, grabbing all the haste you can get your hands on and then just chain mana potting to compensate.


Best and Worst
Best: 5v5 Arena and Sunwell, in my opinion.

Worst: RNG (Mace Stun, Imp Hamstring, Windfury Totem, Frostbite, Resists, Etc), Shamans in PVE, Druids in PVP

Why exactly did Blizzard choose to throw so much raidwide damage at us in Sunwell again? Was it because they wanted to give other healing classes an edge over paladins? I think that was the reason. Paladins were the top healers when BC was first released. Seeing as they're homogenizing everything for wrath - I don't see why they shouldn't give every healing class a strong single target heal and a strong group heal option.

This is a bit silly - perhaps they wanted to actually give other healers something to heal, with their class strength spells? AOE heals like Chain heal, COH and HOTS were designed to be used. Thus we need appropriate raid damage to make them useful. A more pressing issue is that Paladin MT healing is often very underappreciated/taken for granted. They were good at what they do, but people are much less likely to comment on it - than your friendly Shamans using CH/COH to keep the raid alive.

I can't speak for others, but Paladins in my guild often felt second rate to Shamans/Priests for this reason during Sunwell. They can do their job - and do it damn well - but it was still the Shaman and Priest healing that really got the glory. I felt one of the biggest issues for Paladins in general during TBC was transparency. People simply didn't have a reason to notice them doing their job. Ret tooltips weren't updated. Ret buffs simply didnt do anything obvious (You got +crit and +dam), unlike WF/VE where you get fancy weapon proc animations and SCT spamming you with wonderous regen. The same goes for holy.

I would have to say that one of the biggest positives of TBC was Hybrid design. No, its not perfect still... but Feral Druids and Shadow Priests are now recognised as viable members of your raid. We take this for granted now, but it wasn't that long ago where the players were pretty much just laughed at. Moonkin and Ret specs suffered a little in TBC, but WOTLK is looking much more promising in that regard.

Raid healing has been an issue with Paladins in TBC, but that was never their strength to begin with. Their strength is either
1.Spamming FoL as a "casted HoT" and never run out of mana
or
2.Using Holy Light and achieve the highest single target HPS in the game.

When a stream of hots from druids and priests are constantly rolling, it seems like paladins are underpowered, but when you need to keep a single target up with a very limited number of healers, a Paladin suddenly became your best choice because their single target HPS cannot be touched by anyone else.

Problem that has always plagued WoW healing is the fact that people care too much about meters, especially healing meters. While for damage meters you can actually compare, it is very hard to quantify healers. As long as you're doing your job (Shaman keeping the raid up, Paladin and Druid keeping the tanks up, etc), don't worry about the meters.

Zones and Quests
Questing was fun in zones such as HP, Nagrand, Blade's Edge and SMV. I was dissapointed with the zones of Terrokar, Zang and split about Netherstorm. The main reason being that HP, Nagrand, BE, SMV seemed to carve a story around the zone. Zang was "Naga stealing water" ridicule, Terrokar was just plain boring. Netherstorm had some good storylines but the presence of Neutral only factions made me cringe as I had expected BEs to be there in the zone Kael is in.

The Rep grinds are annoying and I am exalted with very few TBC factions. If Blizzard hadn't reduced the rep needed for heroics I would have been unable to run most of them. I love that in Wrath rep gains are not tied to a specific dungeon. Daily quests are good especially the Isle ones.

5-men content
The 5-man content in TBC was boring and bad. The main reason is that 5-man dungeons in Azeroth were lore-rich, TBC it was just a way to get badges. Dungeon stories were never really explained, some of them took too long to complete and just felt like chores.

I like the badge system, I am not a hardcore raider and it helps me get good gear. From my playtime in beta, the Dungeon lore, design has defenitely improved so Blizzard defenitely learned from that.

Raids
I started WoW after TBC was released so don't know about 40-mans, but seeing how we have trouble managing 25-mans at times, 40-man raids for like Archi would be a nightmare. I think 25 and 10 manning is the perfect raid size. Class balance for PvE was definitely a bit off and most fights seem to favor range dps. I thought Loot distribution was fine, we went through BT/MH since 3.0 patch and never had issues with a class not getting loot drops.

PvP
I don't do Arenas, but BGs were allright. Problem with BGs is it all depends many times a random group of people who are playing with so its not in your hand.

Professions
I started with Mining/BS that they turned out to be absolutely useless for me. Honor gear replaced my swords and switched to LW/Ench which gived me a better PvE edge.

Misc
Everything you think that doesn't fit in any of the other categories.

Best and Worst
Best:
1) Raid Sizes
2) HP, Nagrand, BE, SMV Zones

Worst:
1) 5-man content
2) Rep Grinds

Zones and Quests - I thought these were pretty good overall. There were some new mechanics for some quests (ie. bombing runs) and more than enough questing to get you through all the levels. Also the dalies and the ability to put some higher level areas in flying zones was a brilliant way to combat gold sellers. The main annoyance was that so many of the dailies required group quests to access - that seemed unnecessary but I imagine that again, this was done to discourage gold sellers.

5-men content - I especially enjoyed the heroic dungeons and was happy to see some nice challenges for small groups. The badges are a great idea, but they definitely need the "tiered" badge system they are introducing with Wotlk cause the gear that you could get for running heroics/kara was pretty out of control.

Raids - I prefer the 25 man raids over 40 man. Attunement quests were a disaster though, especially requiring 5 and 10 man attunement quests to enter the 25 man raid zones - the logistics of this was a huge hassle. TBC DESPARATELY needed a large entry level 25 man zone similar to MC or Wotlk Naxx. Encounters like Gruul (2 tanks, melee unfriendly), Mag (5 tanks, bunch of warlocks), Hydross (resistance) are all horrible for entry level fights - entry level fights should be something you can do with almost any raid makeup group and requiring people to do silly things like skip encounters to go to Void Reaver or Lurker was pretty annoying.

I did like the way they tuned the content very difficult at first, then slowly nerfed it to allow more access. This allowed guilds to distinguish themselves, while at the same time allowing many people to eventually see most of the content they wanted to.

PvP - I enjoyed the arenas, but they desparately needed the duel talent spec feature because switching back and forth for raiding just became too tediuos after a while. I also felt that class balance was too focused on arenas a lot of the time and they were all to quick to make changes while having adverse affects on the raiding balance.

Professions - I like the BOP epics they give each profession and am fairly happy with the direction they are going there. I still feel like there is a lack of jewelcrafters (the good ones are probably all retired on their beds of gold), I think that the recipes may be a little too hard to get still. Tailoring epics were pretty stupid early on in the raiding game since they basically negated an entire tier of gear. Alchemy definitely needed the overhaul they gave it early on, and the discovery system was pretty annoying (it flooded the elixir market).

Misc - Requiring Revered rep to go into heroics was pretty annoying. I Hated this grind, and they really should have lowered/removed the key requirements much sooner. Early in the expansion, the heroics were difficult enough to keep out the people who were not ready, this is the way it should be.

Shattrah is just a boneheaded design in general. Most players in Shattrah tend to congregate in 4 places:

1. The banks
2. The faction (aldor/scryer) tiers (most people here are just idle or afk)
3. The battlemasters
4. The covered center where A'dal is (again, mostly idle)

Remove the battlemasters and banks from Shattrah, and force players to move to IF/SW/UC/Org/etc for their banking and BG needs. Shattrah should only be a place for you to idle/turn in quests.

Every time I go to the Shattrah battlemasters, there's a ton of people standing around a tiny little platform waiting to get into their next battleground/Arena. Why are the battlemasters consigned to a tiny platform? In every other city, the battlemasters get their own room, or even a whole portion of a city. The Shattrah battlemasters should be moved into their own room (maybe even instanced to reduce lag, like the Deeprun Tram).

Ironforge, for example, has the Battlemasters in the Military Ward. There's absolutely zero reason for anybody to go into the military ward except for the occasional low-level quest, repair services, weapon training, and battlemasters. Even in vanilla WoW, Ironforge lag was mostly in the Commons area, not the Military Ward. This theme continues in all the other cities except Shattrah.

I'd also like to see another hearthstone point at the World's End Tavern. I don't want to hearth back to my faction's Tier, i want to hearth back to the Lower City so I can take advantage of the nearby battlemasters, LC quartermaster, profession vendors, Haris Pilton, etc.

I think the problem with Shat is that while you can port from Shat to the major cities, you cannot do it the opposite way unless there is a mage present. This design made most people, if not all, to set their hearthstone in Shat. The Battlemasters and Bank were really just icing on the cake in this case. Shat would be a lot less crowded if
1.The portals to major cities were removed (this would be stupid)
2.Portals back to Shat are added in major cities.
3.Add some freaking incentives to abandoned cities like Darnassus or Silvermoon
4.Change the forced logout timer from 15 minutes to 10 minutes.

As for the battlemasters, it would be nice to put them on platformed areas, but that would still be abusable for the people that just like to mount on their flyers just to be annoying. Sure, you can use the nameplates, but people are just trying to be annoying in those cases.

Lorewise, a city where the peace between the two factions are enforced is very good. The whole reason I picked a pve server initially was the fact that the horde versus alliance mentality just isn't a very valid one after Archimonde's invasion and presence of the Lich King. The only catalyst for a war is the return of a very angry king in Stormwind.

Isn't that a good thing, though? It was difficult to tune a TBC DPS check tightly because of the huge range of a raid that stacked to the max vs. a raid that didn't stack at all.

By enabling everyone to stack without even really intending to, the range suddenly drops to a difference of a couple hundred RDPS as opposed to a potential several thousand.

This lets devs get away with creating edge-of-your-pants Enrage timers without forcing everyone to do the "Recruit 5 Shaman, Max Warlocks, Exact melee group makeup" shuffling.

...

This really has nothing to do with wanting to be on top of the meters.

Maybe it's due to a general lack of skill to the healers in my guild - but I have been through dozens of different healers through all of BC raiding and the thing that always bothered me the most is if I didn't have a decent enough balance - ie 2-3 Shamans, 2-3 Paladins, 1-2 Priest, 1-2 Druids - I was simply not going to be successful on that particular night. Sure, bosses were still beatable with 5 paladins and zero druids, we worked with what we had, but it definitely wasn't easier. I strongly disliked bringing a player that I knew was sub par only because he was a shaman or because he was a druid and we lacked HoTs or we lacked AOE heals.

I noticed a lot of people aren't happy with the pace that raid content was released. I'm curious to know if that is because those with these complaints are from the "bleeding edge" kind of guilds that completed the game well ahead of the majority (the type of people this site tends to attract).

What I'd like to see is a graph for both Illidan and KJ kill dates by guild to see if the majority of raiders played a well paced game. Anyone know if there is a resource out there like that?

The bleeding edge guilds complain that they have run out of things to do much too fast, but all the rest complains because it makes the difference between the A league and the B league was just so much more obvious. While the A league had completed BT already for months and was waiting for the SWP patch, the B league was still wiping in TK or SSC.

It's just no fun, knowing that you're so many tiers behind in content. In classic it wasn't as bad because there was only ever one new tier of raid every few months, and every release of a new tier usually was accompanied by a nerf of the previous tier. So the difference in classic between the A and the B raiders was usually just one tier, and not two or three like it was the case shortly after the 2.1 patch.

To me, the problem with the raid pacing wasn't that there was too much out there, it was that it was all too easy (post patch that "fixed" SSC and TK). If you absolutely needed the gear from Vashj and Kael'Thas before you had a chance at getting through Black Temple and Hyjal, then it would have worked much better. To me, just because raid content exists in the game, does not mean you are ready to do it. I always prefered the EQ style of gearing up in previous zones, though I know this isn't the paradigm that Blizzard follows.

I mostly have comments on 5-mans and raiding.

I hate the linear corridor style 5 mans that were in abundance in TBC. An instance can be linear without feeling linear, like BRS, Dire Maul, and Maraudon. I have been on media blackout for WotLK as far as instances, raids, and lore but I hope they addressed this issue.

For raids, the one thing that I would like to see implemented is a way to bypass the beginning of a raid instance if you have done it many many times. I am raid leader for a guild that raids two nights a week. We got up to Illidan Phase 3 before 3.0 and the limiting factor on our progression was clearing BT fast enough to have time to work on Illidan. We eventually buckled down and shortened our clear times substantially but hitting the back half of some instances can be difficult on a short raid schedule. Even a one use item like a key where we have to clear the instance one week, then the next week can unlock the final boss (or two), then reclear the week after that again would be preferable to the current system.

This might also help some guilds who would have to choose between farming Naxx just for some drops from KT and working on the next Raid. I know after we killed Kael and Vashj we hardly ever went back to SSC/TK for them since we just didn't have time.

I would argue that this would mean the pacing was good for the majority of raiders, if data backs this up. There were the handful of guilds that completed content much faster than what was intended, and the majority moved along at an appropriate pace and didn't have a ton of time where they had nothing to do but farm BT.

And that is what I would like to see in a graph with data from WowJutsu or something

That honestly doesn't sound like decent pacing.

The (competent) majority of raiding guilds should be moving into new tiers as they're released; they shouldn't still be wiping in the old tier months after a new one becomes available. Ideally the rate at which Blizzard releases content and the rate at which your average (again, competent) raiding guild consumes it should be equal.

A significant reason (although certainly not the only one) that no one came back to kill Vashj and Kael was that they required a full instance clear and dropped items of lower ilvl than the first bosses of the next instance. The first part was true in Classic, but the second part was not. People cleared MC while killing Nefarian because the Tier 2 pants and other items Ragnaros dropped were better than most of what was available in BWL. While Kael and Vashj certainly had a few items that wouldn't be replaced for a while, on the whole the bosses you opened up in Hyjal and BT dropped larger upgrades per time spent while nothing matched the quality of Ragnaros' loot until Chrommagus (IIRC). Similarly, nothing matched Nefarian's loot until Huhuran, and nothing matched C'thun's loot until Sapphiron. There was such a significant difference between the ilvl of the mini-bosses and end boss that it made sense to continue to farm the end boss.

Now, that's not to say there isn't something good about the TBC system. It meant that people weren't forced to clear the entirety of the instance just to get to the good loot off the last boss, but given that TK and SSC were designed almost explicitly with being able to skip bosses and go directly to the ones you want it seems strange that it took so long for them to let people go directly to the last boss given the outcries about MC. And of course the rest of the instances were designed more linearly, if not completely linear.

That last point reminded me of the lack of optional bosses like Viscidus and Ouro. Outside of the 20 mans, only AQ40 had optional bosses. Once again, the first small raid (Kara) had lots of optional bosses while for ZA the best you could say was the optional boss was the chest timer. Why aren't there more of these guys? Why must we wade through the entire instance killing every boss even if there are no drops anyone wants in order to get to the good stuff? Karzhan was very well designed (in my mind) for this purpose: there were very, very few required bosses. In theory, you only had to kill Moroes, Opera, Curator, and Chess to get to Prince. The entire linear progression was 5 bosses (only 4 of which were actually real encounters) out of 11. Sure, Shade of Aran was very nearly a requirement, Nightbane was required for attunement for a while and Attumen was an easy pushover warm-up, but they were all still optional along the main path that led to the tier tokens and to the best ilvl loot, which was from Prince.

Naxx has no optional bosses, but could they not have redesigned the instance to not require killing at least some of the mini-bosses in each wing and only leave the last ones? The most I've seen of Naxx as a player is clearing to Razuvious, but the layout of the instance suggests killing some bosses open doors and for others the room is large enough that they could just be positioned somewhere that could be bypassed (like Morogrim). The whole point is to not force people to kill bosses that they don't want to, but still maintain the whole idea of having to "clear" each wing to open up the last two.