I'm looking forward to seeing the sweeping changes across ALL of the game world, not just Azeroth. Outland needs to be heavily retooled, and it'd be fun going back to see it in a different light. Same thing for Northrend, given the events of ICC.
Then there's all the things that have happened since regular WoW that we have not heard much on until now. Like saving the druid in the Wailing Caverns, now he's out saving the Barrens. It's going to be nice to finally see changes across the land.
Finally, my personal favorite is the idea of being able to play as a Goblin. I've always been annoyed at Gnomes, with their coy little phrases and attempts to be cute that make me want to toss them off a cliff. Goblins on the other hand, well, they're pure capitalists, and while Gnomes are about building things that would put the Doozers to shame, the Goblins on the other hand, as we all know, are all about blowing the living crap out of stuff. Throw in the fact that Horde gets Goblins, and it's all gravy.
I could care less about the Worgen.
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"Do you know what "nemesis" means? A righteous infliction of retribution manifested by an appropriate agent. Personified in this case by an 'orrible c*** : me."