I think it's really hard to judge the new rune system with the limited information we have so far.

The main reason being that we don't really know how the cost of abilities is going to change. A while ago GC made a comment stating that they wanted to make Death and Decay a more tank centric ability, costing a single blood rune. Maybe he was already having this system in mind.

The same could be true for abilities like obliterate and scourge strike. Or the amount or RP generated per rune.

I think with the current information in mind we can say a few things though:

1) We'll very likely have more free GCD. Ghostcrawler already stated we would. I know quite a few people are against this, because DK are one of the few classes that actually press some kind of button constantly. But I think it's a change for the better. I see it likely that we'll use about 2-3 rune abilities per 10 seconds and another 1-2 runic power abilities. That's already 4-5 GCD which equals 6-7.5 seconds. Add in the possibility of having "free cost" abilities, or cheaper abilities and that will only go up.
That is still much more than most other melee classes do.

On top of that comes the added effect that special attacks might turn into actual special attacks again. I'm not sure about others, but I personally never really liked the concept of your special attacks doing 2/3th of the damage of a white swing.

2) Another advantage that I'm not sure anyone here touched yet is flexibility.
Not only does this mean we lose FAR less damage in mobile fights. It also means we can strategically handle our runes.

Think of fights like XT-002 where you have set burst phases. Pooling up some extra "rune buffer" could play in on some more strategical gameplay. An element that DK resources have been severely lacking in WotLK. Currently you HAVE to burn your stuff or you're simply losing damage.
Another example is Lich King, where you might want to pool up slightly before the val'kyrs come. Imagine waiting 15 seconds instead of 10 seconds before you continue your rotation. Instead of having to wait 5 seconds between rune sets, you can now chain 6 runes in a row.

Again though. It is really difficult to see the final impact without knowing what new abilities we get, and how old abilities change.

One of the concerns I read on the EU forums was that disease applying will now create really dull rotations and long deadzones.
Because basically if things stay unchanged you get a rotation consisting of: PS > IT > BS.
And that's it. If you are doing 5 mans, you might very well see that rotation on every trash pack without much else.

Again though that's a bit unclear since we don't know what and how that's going to change.

You are assuming like many others, that for some reason they are leaving the rune cost of abilities unchanged.

I wouldn't at all be surprised is something like obliterate will instead of 1FU pair simply cost 1 frost rune. Then death runes get their value back right away.

You have to think outside the box, because they are clearly going to have to overhaul many of our abilities.

I like the idea behind the rune system change, and can see the reasoning behind the single tanking tree (with hopefully some useful abilities for dps in the early tiers).

The changes seem to be lacking in specifics compared to some of the other classes, such as what the form of the unholy mastery is going to be (it's not phrased like some of the other increase x masteries). With such dramatic an overhaul I guess they're even pretty vague on how the changes will play out.

The more I think about it, I really like the idea behind the new rune system. It allows for much more dynamic play. For the most part you'll have a 10 second window to use your runes in, which is a great improvement over the way it plays now.

I found it quite suprising that they didn't mention any changes to our diseases. Almost every other class had the standard haste / crit will apply to most HoTs and DoTs. Haste will increase the number of damage ticks. Furthermore all DoT reapplications will act like the GoD does now, and just reset the duration. This means we will want to refresh our diseases as they're about to expire, there is no cost for clipping them, and letting them drop off is a bad idea as you'll likely lose part of a tick. Haste is also going to increase the rune refresh rate, so we're unlikely to have anything resembling a 20 second cycle. With the extra freedom in the rune system we won't need one though, but it will take a bit of getting used to.

I'm inclined to suspect while we'll have some free times in our cycles, unless haste is changed to reduce melee gcds, we won't be in much danger of straying into pushing a button every 5 seconds territory.

Some points of interest to me:

1) The masteries are for melee damage. How do you balance that given that unholy will be doing more magical damage than frost (probably not too hard if they limit the max bonus).

2) What happens to pets. They're supposed to be a focus of the unholy tree, yet for the most part our pets are just viewed as cooldowns or passive damage in pve at least.

3) Why hasn't expertise been modified in some form or just removed completely. While the mechanic behind it isn't too hard to explain, the way expertise rating gets converted into expertise and then reducing your chance to have an attack avoided is rather awkward, Especially considering it shares a gem colour with the main dps stats.

Given the information present, I don't think the Deathknight's playstyle will change from being global cooldown bound. In fact I think we're more likely to find ourselves in Unholy presence straining for more. The problem is the Haste changes.

Looking at Consider's chart we're presented with a number of possible outcomes:

1. We get new buttons to press to fill in those empty gbc's that are resource free. Thusly no change.

2. Runic power costs are adjusted to some magic number, we fill up those free gbc's with Rp abilities. No change.

3. Haste, as stated, affects Rune regeneration, theorycrafters find the Haste "Cap" to provide enough Rp for #2. No change.

4. Haste affects Rune regeneration and the Gbc, play in fact speeds up, higher Haste "Cap" go to #3. No change.

For 3 and 4 if Haste can actually arrive at the appropriate values then we might even see people moving into Unholy presence to hit even faster causing play to actually feel more piano like, and looser due to the 200% wiggle room, as opposed to less. Blood might even need it as a third cap to maintain threat giving us a distinctly warrior "my poor poor hands" flavor.

The only way we'll actually see those large spaces between hitting abilities is if the Stat-to-Ap coefficients are so large on other stats that we don't seek it out on gear which will probably negatively impact the other plate dps classes. Or, Haste has such a small coefficient that it feels like a punishment if our gear has it at all.

Either way, can't wait for the juicy details and what some of the more masterful Theorycrafters conclude.

*edit: Consider mentioned most of this earlier.*

My interpretation of the rune changes is that we are resource locked where a rune off cooldown is a waste, and that in turn is causing the gbc lock. This frees up space for new mechanics for us to use, but once those are accomidated player psychology tells me that people will try and tighten those up to the absolute max. While the new rune setup prevents us from being penalized by waiting it does not encourage waiting when you don't have to, so why would players not try to maximize haste to the point of being gbc bound?

Also, I likely am reading entirely too far into the presented info, but Frost's Mastery Bonus seems rather ambiguous. Generating runic power is already "appealing", I can't actually see how it is not appealing, much less needing to be made more so. If they meant easier, why not just say so. The ambiguity leaves open a different mechanic unrelated to how much rp you gain for something similar to new arcane mage mechanics.

I am probably so wrong it makes babies cry, but I can't imagine 4 second or more gaps of doing nothing to survive long through beta without negative feedback or an amazingly good/fun reason.