Things are going to be somewhat different in Wrath of the Lich King, although Destruction is still pretty much the tree for blowing up things into oblivion. A lot of the talents incentivize mixing up spells and steer away from chain casting Shadow Bolt. A talent deep in the tree also rewards keeping a pet out. The tree is essentially a crit tree, the tree to make things go boom, although Blizzard clearly wants Destruction Warlocks to throw other things into the mix.
One of the obvious changes was the move of Bane to the first tier, making it easily accessible by other specs. Cataclysm was moved down and changed to a 3-point talent for a lower reduction in mana but with added hit chance for Destruction spells. This is an odd change for me considering Blizzard has been moving away from Hit talents, and a 3% cost reduction is negligible. Molten Core, a new talent on Tier 2, encourages Warlocks to mix up their spell rotations with DoTs, although I'm not sure if activating the GCD to apply several DoTs might is worth the 10% increase in Fire spell damage, specially with a mere 15% proc. Of course, Shadow Bolt procs this, too, but the theory is that you won't be spamming Shadow Bolts -- and it won't make sense to proc it without throwing Fire spells into the rotation.
The PvP-centric Aftermath was buffed to a two-point talent for the same effects. The tree also gains more point efficiency with the consolidation of Improved Fire Bolt and Improved Lash of Pain into Demonic Power. Most Destruction builds skip those two talents anyway, so I'm not sure Demonic Power is any more enticing. For one thing, an improvement to Lash of Pain is pretty useless considering Succubi are almost never used for DPS due to their fragile nature. I mean, Lash of Pain is a melee range spell. Either Demonic Power needs to be buffed somewhat or Lash of Pain changed to actually be attractive enough to use.
Another big change was the swap of Ruin and Devastation in the tree. This makes Ruin available to more builds earlier in the tree. I'm still underwhelmed with Improved Searing Pain simply because it's three points for a situational spell. Searing Pain is great for juking Rogues into locking you out of Fire when you're SL/SL, and it's great for tanking Leotheras the Blind, but otherwise the high threat makes it almost a strictly PvP spell as it has no facing restriction and a relatively quick cast time.
Nether Protection was revised to proc off any spell and grants damage reduction against the school of the spell that procced it. This is much better than the two-school immunity of the original spell and makes it a good choice for PvP. Speaking of PvP, the PvP talent Shadowfury was properly changed to instant cast and buffed to a 3 second stun. In other Destruction news, Soul Fire's inane cooldown has been removed. So if you want to chain cast a 6 second nuke (4 seconds with Bane) and burn through Soul Shards, you now can! Whew. That was just for the old stuff. Now we'll take a closer look at the new talents in Wrath of the Lich King aside from Molten Core and Demonic Power.
Improved Soul Leech
Requires 35 points in Destruction
Your Soul Leech effect also restores mana to you and your summoned demon equal to 2% of maximum mana.
Any source of mana is a welcome one, although a 2% return from a 30% proc is extremely low, specially for a class that can already Life Tap. You also have to spend mana in order to gain mana back, which I was never a huge fan of. Considering how mana-hungry Destruction can be, it's not a bad talent, it just needs to return more mana if it's to be worth the investment.
Requires 40 points in Destruction
When you cast Conflagrate, the cast time of your next three Destruction spells is reduced by 30%. Lasts 15 sec.
A Destruction Warlock's biggest enemy is casting time. So when a spell that tempts Warlocks to cast Immolate and Conflagrate in order to get reduced casting times, you can be sure it'll see a lot of players dabbling with it. Think of it as a personal Bloodlust for all Destruction spells. The cool thing is that you can keep the Backdraft buff up indefinitely. The uncool thing is that keeping track of all your timers will now be a headache because, honestly, this talent makes Destruction hell of a lot more fun to play. 3 points here is pretty much mandatory for raiding.
Requires 40 points in Destruction
Increases the damage done by your Imp by 15%, and all critical hits done by your Imp have a 100% chance to increase your spell critical hit chance for your next spell by 20%. This effect lasts 8 sec.
This talent was nerfed somewhat to grant a mere 20% increased crit chance from a sure 100%, but the real question is whether keeping an Imp out will grant more DPS than Demonic Sacrifice. I don't have hard numbers, but my money is on an emphatic yes. Of course, this necessitates buffing up your imp all the way until Unholy Power to essentially make it a whiny little cannon. This talent should see your crit rate spike up significantly so that the biggest problem is that Empowered Imp bloats Tier 9 unnecessarily. So what if you skip Shadowfury? You've still got six mandatory talent points to spend on this tier. Plus, the icon is so darned cool.
Fire and Brimstone
Requires 45 points in Destruction
Increases the damage of your Immolate spell by an amount equal to 15% of your spell power, and the critical strike chance of your Conflagrate spell is increased by 25% if the Immolate on the target has 5 or fewer seconds remaining.
I just don't know about this. If you just spent six points in the previous tier, you really won't have too many points to spare to max this talent out. The talent feels extremely clunky, with the necessity to watch the timer on Immolate and forcing the Warlock to let Immolate run its course. I understand that Blizzard wants us, forces us to use Immolate -- but this is just silly.
Requires 50 points in Destruction
Sends a bolt of chaotic fire at the enemy, dealing 1036 to 1314 Chaos damage. Chaos Bolt cannot be resisted, and pierces through all absorption effects.
The best part of this spell aside from the wicked animation, I think, was Chaotic Mind. Unfortunately, that effect was removed in the last build and I'm not sure we'll see it come back in some form. I wish it comes back, though, because we really need to see Soul Fire see more action. Anyway, the spell is still a definite boost in DPS because it ignores resistances and pierces through absorption effects like Power Word: Shield. The damage is from the Chaos school, which is actually all schools combined. While this is great as far as bonus effects is concerned, this also means a well-placed Kick while casting it means you're a sitting duck for the next 5 seconds. This makes it a horrible spell to use in PvP. It's a decent DPS spell, but as a 51-point talent it's pretty underwhelming without Chaotic Mind.
Destruction still feels weird. I haven't figured out the optimal spell rotation with it, partly because everything is in flux and partly because I really want to make everything work together. Deep Destruction rewards Fire almost too much, and Shadow Bolt falls by the wayside. Destruction should feel like a mix of both Fire and Shadow, and Molten Core simply isn't enough to make that work right now. Another thing I can't quite figure out is why Shadow and Flame is a prerequisite for Shadowfury. Shadow and Flame is a largely PvE talent and Shadowfury is a PvP talent. It punishes PvP builds by requiring points in Shadow and Flame. Overall, the tree still feels like it needs more work, but with Chaos Bolt and Fire and Brimstone only recently working and testable, I'm certain we've yet to see it explode in all its infernal glory.