Destruction is supposed to be the most chaotic and unpredictable Warlock spec. I don't know that it has always lived up to that, but we'll see as we look at how the spec's changes will work. All Warlocks are returning to Soul Shards as their secondary resource, which I'll be honest, kind of bums me out, as I thought that Demonic Fury and Burning Embers were cool and very clear ways to distinguish the specs.
Destruction is still going to be the Warlock spec that goes far more into direct damage than DoTs, and I don't think it's getting any really profound changes to the overall theme of the spec. If you're Destruction, you just want to watch the world burn.
As always, this is based on an early Alpha build, so there can and almost certainly will be changes.
Incinerate will remain your main filler spell, with a 2-second cast time to deal Fire damage to a target.
Immolate has a 1.5 second cast time and deals Fire damage to the target, then doing additional Fire damage over 15 seconds. Immolate crits will grant you a Soul Shard.
Conflagrate is instant-cast, with two charges and a 12-second recharge, dealing fire damage to the target and granting a Soul Shard when it crits.
Chaos Bolt costs Soul Shards (currently it says 0, but I think it's really 2) and has a 3-second cast time, dealing massive Shadow damage to the target. It is guaranteed to crit, and does additional damage based on your critical strike chance.
Rain of Fire has a 2 second cast, dealing Fire damage to the targeted area over 8 seconds (much like Blizzard, it's Frost Mage counterpart, it's no longer a channeled spell, and allows you to do other things while it's up.)
Havoc has a 20 second cooldown and is instant. For the next 8 seconds, all your single-target spells will also hit the target with Havoc on it.
Summon Doomguard and Summon Infernal now only have 3-minute cooldowns and last 20 seconds (I assume the cooldowns are shared, like they are now.) The Infernal's still for AoE, dealing a blast of AoE damage when it's summoned and then continuing to deal Fire damage while it's up and smacking your foes. Doomguards will shoot shadow damage at the target you summoned them to shoot at.
Mastery: Chaotic Energies increases the damage your spells do, by a random amount up to the maximum determined by your mastery stat.
Much of this should look very familiar, and crit remains a very potent stat. Before we get into talents and artifact traits, the basic shape of the rotation should be something like this:
1. Maintain Immolate on the target at all times.
2. Chaos Bolt if you have just under full Soul Shards (I think the max will be 5, so at 4.)
For AoE, you'll want to mark an alternate target with Havoc right before you cast Chaos Bolt - you might even try to get off two (or three if that's possible - it won't be if the Soul Shard cost is 2.) You'll also want to get Rain of Fire running on your targets.