Stealing a leaf from Aldriana's book. Sourced from MMO/WoWHead and written in my own words.

Some of these changes (glyphs) are no doubt going to shake things up a little bit.

Core Abilities

• Curse/Aura of Enfeeblement: Tooltip updated to 10% physical damage reduction.
• Unending Breath: Tooltip fix for Soulburn/Affliction.
• Spell Lock (Felhunter): No longer silences. It's only an interrupt. (IE - Reverted to Classic functionality.)

Talents

• Soul Leech: No longer heals, but provides an absorption shield to you and your pet equal to a portion of the damage done by listed spells, lasting 15 sec.
• Blood Fear: No longer an instant Fear; requires 20% of max health. "While active (60 sec), any time an enemy melee attack deals damage to the caster they will become afflicted by Fear. 1 charge. 30 sec cooldown"
• Grimoire of Sacrifice: The damage bonuses to spells were slightly nerfed for Affliction and Demonology (was 25-50%/50% now 20-45/45%, respectively). Also, Warlocks gain Whiplash instead of Seduction from sacrificing a Succubus.
• Grimoire of Service: The pet summoned by this ability instantly uses a special ability the moment it's summoned.
  • Imp: Singe Magic on the master.
  • Voidwalker: Suffering/taunts the target.
  • Succubus: Seduces the target if Humanoid.
  • Felhunter: Spell Locks the target.
  • Felguard: Stuns (Axe Toss?) the target.
• Sacrificial Pact: HP consumption now 25% of current from 50%. Shield amount (200% of consumed hp) the same.
• Kil'jaeden's Cunning: Active component removed; it's now completely passive.

Glyphs

• Glyph of Soul Shards: Renamed Glyph of Drain Life; increases Drain Life healing by 30%. Former effect (4 Shards) is now baseline for Affliction.
• Glyph of Burning Embers: Renamed Glyph of Ember Tap; increases healing of Ember Tap by 50%. Former effect (4 Embers) is now baseline for Destruction.
• Glyph of Demon Hunting: Tooltip fixed to make it clear we should have Sleep in Dark Apotheosis in place of Fear.

The prime glyphs are arguably the biggest changes out of everything. These two glyphs are mandatory for Affliction/Destruction, for obvious reasons, which is exactly what Blizzard has said they don't want to have happen for Prime Glyphs. It was only a matter of time before we got this. I'm VERY curious how the sims change on account of the cap to three shards/embers now.

Official patch notes confirm that these glyphs are now simply baseline. Affliction and Destruction now simply get 4 Shards/Embers by default. (Edit: Damn you Daimonas!)

Looks to be almost exactly a 2% DPS nerf to Affliction.

Also, it's Destruction that took the other hit, not Demonology. Demonology's Sacrifice benefit is untouched (which has no effect, since no Demo warlocks use it).

So, the warlock changes in 5.2 are pretty much just nerfs across the board. With the lonely exception of Soulburned Unending Breath. Colour me not so surprised.

Since I don't do much PVP I care little about the Curse of Enfeeblement, Spell Lock or Blood Fear nerfs. The latter of which certainly seems quite severe, but it was expected after GC mentioned that instant cast / uninterruptable CC is probably on the nerfing block when they continue to balance PVP.

Soul leech is the weakest component of our passive self heals triage, of which quite a bit is wasted as overheal in my experience in a normal raiding situation (depending greatly on the situation/encounter of course). So it actually might be a good idea to turn a portion of the self heal to absorption. It'll be interesting to see how it'll play out (what the % will be, is there a cd etc.)

The change is 5 percentage points, not 5 percent. Not that the difference between the two is all that huge (and I'm sure you meant the former).

Removing the glyph of Soul Shards sure feels like a pretty big quality of life nerf. And on certain kinds of fights, like Will of the Emperor where you get 4 small adds, it will certainly be very annoying.

However, even though it makes timing tighter, sitting on shards while waiting for more procs more difficult and resources less abundant after a drainsouled kill, it's not a very big nerf to actual DPS.

I ran a few 50k iteration sims with the newest version of SimulationCraft (510-7) on my own affliction profile (which is probably quite close to the Tier14 Normal warlock profile, ilevel being between 493 and 495, with the 4p tier bonus) and the results were:

Single target
109418 dps with 4 shards
108888 dps with 3 shards
530 dps or 0.5% nerf

2 targets
131243 dps with 4 shards
130820 dps with 3 shards
423 dps or 0.3% nerf

4 targets
155386 dps with 4 shards
153769 dps with 3 shards
1617 dps or 1% nerf

8 targets
273455 dps with 4 shards
268949 dps with 3 shards
4506 dps or 1.65% nerf


Edit note:
Ah, it seems folks replied with new info while I was writing my reply. So you can just ignore the sim results.

Blizzard's choice of making 4 resources the baseline is the only right one. Lowering players' perceived quality of life is rarely a good design direction. And now we have one more prime glyph spot to fill with something that is actually a choice.

Based on the wording of the datamined tooltips, it's the same percentage as previous (20% for Aff and Demo, 10% for Destro), and I have a hunch it'll work like Divine Aegis, where new shield applications simply roll into the current one. Thus if you land a 500k Chaos Bolt (50k shield), take 25k damage, then land another 500k Chaos Bolt, your shield would have 75k remaining.

This is a nerf to actual self-healing but a buff to net survivability, because, as you pointed out, Leech is often overhealing. There'll probably be a cap on the shield, though.

That's what made me question it, because Affliction's Sacrifice is 50% flat, not a range. Demonology is a flat 30%, Destruction is a flat 25%. Destruction went down to 20%, Affliction to 45% (which explains the range noted, as it currently *is* 25-50%, across the specs, and now will be 20-45%). Demo is staying at 30%.

This isn't the first one to have improper specs notated in the tooltip. For example, Grimiore of Supremacy annotates the Wrathguard for Destruction, not Demonology (Demonology is annotated with Affliction). Grimiore of Service similarly misattributes the Felguard to Destruction.

What it looks like, from the tooltip, is that it's supposed to have four sections, general ("increase the power of many of your single target spells by 20% to 45%"), then a section for Affliction, Demonology, and Destruction, in that order, specifying the actual percent for that spec and the details. Somewhere that framework got muddled, and the first section is mislabeled Affliction, despite it not supposed to have a label, the next is labeled Demonology, despite the fact that it's Affliction's bonus, the next Destruction but with Demo's number, and the actual Destro section simply omitted.

So it was in fact Affliction and Destro. The Affliction nerf makes sense, since Sacrifice is miles ahead of the other two Grimoires for that spec. The Destro one baffles me a bit, as Sacrifice was already nearly dead even with both Service and Supremacy for that spec, and Destro is also the bottom of the pile on the PvE side and could use a pretty solid DPS buff to put it back on level.

On a side note, nerfing Sacrifice wouldn't make sense in the slightest for Demo, since literally no Demo locks use it (and it's a 6-7% DPS loss over either of the others to boot). Then again, it would be like nerfing Sac Pact, and they did do that (unless they are also planning on increasing the HP->Shield percentage, or reducing the CD, either of which would work with the new 25%), so who knows.

Just tested on PTR and the cap is the maximum health the user has. I doubt someone will even go close to that, it requires a fairly long time to build up.

From the PTR patch notes as of Jan 17:

Core Abilities

• Fel Armor no longer provides bonus armor; it now reduces damage taken by 10%.
• The Imp's Blood Pact ability has been folded into Dark Intent.

Talents

• While active, Burning Rush now also prevents movement impairing effects from reducing the warlock’s movement speed below 100% of normal, in addition to its other effects.

Glyphs

• New Glyph: Glyph of Ember Tap. This glyph increases the healing gained from Ember Tap by 33%, but causes Ember Tap to heal over a period of 10 seconds.
• Glyph of Unstable Affliction changed. This ability now reduces the cast time of Unstable Affliction by 25%. (No effect on GCD)

Affliction

• The backlash of Unstable Affliction is now a guaranteed crit and deals approximately 15% more damage.
• The Tier 15 two-piece set bonus has changed; it now causes Dark Soul to incresae the duraton of Haunt by 4 seconds.

Cosmetic

• Blood Fear has a new visual and sound effect, and has a visual and sound effect when the proc occurs.
• Chaos Wave now have a new visual.

Most of these new changes are PVP oriented, though the 10% additional reduction to incoming damage is quite welcome. Warlocks have also gained additional flexibility in providing the Stamina buff in the absence of a priest.

Does the changes mean that Demo is now going to be most viable spec for raiding?

Not mentioned above, but Soul Leech has an upper cap at 100% of the warlock's HP.

More hotfixes applied this morning by Blizzard, taking aim at Affliction and Demonology's multidotting strength.

• Corruption damage reduced by 25%.
• Doom damage reduced by 25%.