Warlocks got a pretty massive revamp in Mists of Pandaria, and I think it was very good for the class. It looks like some of those changes are getting rolled back - which is perhaps a little strange, given how the revamp had done such a good job of distinguishing the specs - but I think that they're still moving in a direction that keeps the specs distinct. Once again, I'll have to get these changes in my hands. The main thing is that all Warlocks will once again be using Soul Shards, presumably with the UI element introduced in Cataclysm, though it looks like they'll work in a far more intelligent way.
Aff's still focused on DoTs. The main change, I think, is that there's going to be more of an emphasis on DoT damage, and less direct-damage to compete with it.
Corruption and Agony look more or less the same, but Agony will now have a chance to regenerate a Soul Shard when it deals damage, while Corruption doesn't. To encourage multi-dotting, all your Agonies will be able to regen shards.
Unstable Affliction now costs a Soul Shard, dealing a strong amount of damage. It still has the penalty for dispelling it, and if the target dies while afflicted, you'll get your Soul Shard back. It only lasts 8 seconds now.
Drain Life is the new Affliction filler ability, dealing 50% more damage for each of your DoTs on the target.
Mastery looks the same, increasing the damage of your three DoTs.
Sample Talent: Contagion
After you cast Unstable Affliction, you get to cast another for free.
So Affliction looks like it's getting a bit simplified, without Haunt. Essentially you'll stack DoTs on your targets and try to put Unstable Afflictions on everything. As a reminder - talents are going to be much more spec-specific, so you'll likely be able to build on this core.
The huge difference here is that you no longer have Metamorphosis. Demo is a whole lot more focused on summoning and empowering demons. You'll still deal some damage yourself, but there's far more focus on your demons.
Shadow Bolt remains, but it now generates a Soul Shard.
Call Dreadstalkers is a 15-second cooldown costing 2 Soul Shards that summons a pair of Dreadstalkers to attack the target for 12 seconds (I wonder if there will be some proc that resets this cooldown.)
Hand of Gul'dan has a 1.5 second cast time now, but has no cooldown - except that it'll also cost 1-5 Soul Shards, doing strong AoE damage to and around the target and summons a Wild Imp for every Soul Shard consumed.
Demonic Empowerment is a spell with 3 charges and a 12 sec recharge that increases the health and haste of up to three of your active demons (preferring the strongest) by 50% (presumably this will be your Fel/Wrathguard and your Felstalkers.) This lasts 12 seconds, so you can keep it up indefinitely, but with multiple charges, you'll be able to get more of your demons empowered.
Mastery: Master Demonologist
This now affects Demonic Empowerment, adding a straight damage-increase to go along with the haste and health.
Doom is still around, though it looks like it's a bit different, dealing massive damage after 20 seconds (a bit more like its original design) and granting a Soul Shard once it deals damage.
Demonwrath is a channeled ability that looks a lot like Hellfire except that the damage comes from your demons. Each individual demon might not deal a lot of damage (which is now shadow as opposed to fire) but with a big swarm, you should be dealing a lot. Also, each time it deals damage, you have a chance to generate a Soul Shard, which I suspect means that weaving this with Hand of Gul'dan could get ridiculous.
Sample Talent: Implosion
Causes your Wild Imps to be violently yanked to the target and explode, causing moderate AoE Shadow Damage.
Personally I'm sad to lose Meta (though I'm super happy about Demon Hunters) and the gameplay surrounding it. But this new version of Demo - which is practically all-new - looks like it could be a lot of fun. I'll miss gradually growing demon horns and such, and I kind of hope they do something in the UI to distinguish the Soul Shards of the various specs, but I'm not holding my breath.
Destruction doesn't seem to be getting a ton of changes. Mainly Soul Shards will just be a resource that comes in more discrete units.
Incinerate is basically unchanged. Immolate and Conflagrate work similarly, but now generate Soul Shards. Conflagrate is a guarantee, while Immolate crits have a 30% chance to do so.
Chaos Bolt costs two Soul Shards.
Mastery: Chaotic Energies is kind of funky, increasing Destruction spells by up to 40% baseline, randomly. So it has a the potential to be really powerful, but I wonder how often you'll get the max boost.
Channel Demonfire, which is an AoE cooldown that launches 15 bolts of Felfire at Immolated enemies over three seconds.
The reversion to Soul Shards for Demo and Destruction is kind of jarring, especially as they try to make the various classes and specs more unique. Still, Demonic Fury was always tied pretty intrinsically to Metamorphosis, and Burning Embers were maybe a little dull.
Demonology is clearly getting the biggest changes here, and I think it'll take some getting used to. I like the ideas they're working with, though one thing I wonder about is how they plan to make some of the lesser-used minions more interesting.
Next up will be Death Knights, pretty soon actually.