All Warlock specs look pretty strong in their own right. I have gripes about individual talents or mechanics, but on the whole I think they've taken everything in an appropriate direction.
1) Soulshatter needs to be unresistable. With Cataclysm now adding spellhit in addition to Suppression Blizzard is steering us towards running 13% hit instead of 16%. The problem lies in that Soulshatter is neither Affliction nor Destruction- requiring we run 16% hit anyway... For an aggro wiping ability with a significant cooldown of 5 minutes I don't think Soulshatter being unresistable is at all unreasonable.
2) Felguard/Ruin looks to be THE premier raiding spec. They really went all out to make Demo viable. Fel Synergy will be great for keeping the FG alive without having to waste time with Health Funnel. Demonic Empowerment looks quite nice as well- though the duration for the effect remains to be seen. My guess is ~10 seconds. Need I even mention how nice Demonic Pact looks to be. Definitely going to want one Demo lock per raid.
3) Destruction got kicked in the junk with the Demonic Sacrifice nerf...but in the long run I think the old DS being gone is good for the development for the class. It remains to be seen how well Destro will stack up in the raid game but I'm betting that it will be the #1 DPS spec so long as the imp can stay alive. That being said Phase Shift needs to be changed from a total damage immunity to a 100% AoE avoidance. This will allow him to DPS in raids and act as a mana battery for Affliction, but keep him from being able to attack with impunity in PvP as he will be vulnerable to single target attacks.
4) Affliction looks pretty strong overall. I would have done a few things differently but on the whole I'm satisfied with the changes.
a) Fel Concentration is still a very bloated talent that either needs to be brought down to 2-3 ranks, or affect all Affliction spells.
b) The new Amplify Curse is in a word...interesting, although I can't really hop on board with the implementation simply because CoA/Doom really don't get a whole lot of use in the arena/raid game what with us using CoT/CoX in PvP and CoE/CoR in raids. I'd scrap this implementation and bump the cooldown back up to 3 minutes and have it allow your next CoA not count towards the one curse-per-target limit. (sure it's an old rehashed idea of mine but a sound one if I do say so myself)
c) I'm still not the biggest fan of Death's Embrace as thematics go...but I can live with this one I suppose =P
d) Haunt. I love the new implementation. It's viable for both PvE and PvP and fits with Affliction quite well. However, to address the issue of DoTs not scaling with stats other than spellpower I would tweak it. Currently it increases DoT damage by 15%. I would instead make it increase DoT damage by 10% *plus* 50% of your crit chance. This would effectively allow crit to effect DoT damage. So at 10% spellcrit you would break even at 15%, at 20% spellcrit you would hit 20%. It would be an easy way to work crit into some usefulness. Still, Haunt seems to be very strongly implemented. Thumbs up.
5) Pet Scaling. Maybe we'll see more of it. Rumors are floating around that Hunter pets are getting seriously looked at as far as scaling off stats is concerned Maybe our pets will inherit our spellhit, penetration and more of our stam/int/spirit. If we're really lucky, Resilience, but I'm not holding my breath on that one.
6) Finally, the Fel Armor/Demon Armor changes. I'm all for them, actually. I like the fact that they're creating a distinct PvE/PvP armor type. Fel Armor in particular, giving a base amount of spellpower, 30% of spirit to spellpower, and 30% spirit regen while casting makes a great deal of sense. Homogenizing gear will be a great thing- if any only if Blizzard does a good job at making everyone want the stats that are on said gear. This will do that for Spirit. They just need to work on Crit...