Well, despite only having my laptop right now (though with a new SSHD that helps a lot,) I just had to start my Demon Hunter character. I played through the starting experience - I'm sure I'll take my time a bit more the second time around when I do my Horde one - and now I'm in Stormwind (well, until the World Server went down.)
One thing that's interesting is that the starting cinematic is, for the first time, not that guy (actually I think they switched voice actors after the original one died, but the new guy does a good impression) explaining your race/class to you. Instead, you begin with a first person POV shot of Illidan telling you about your mission to Mardum and then sending you through a portal while he deals with these Azerothian heroes.
I'd say about two thirds of your starting experience is on Mardum. You kill demons and get your new abilities that way (not sure if this works for Vengeance - I just went Havoc the whole way.) Eventually, you battle the Spider Queen Tyrannia on her ship, the Fel Hammer, which flies above Mardum, and head back to the Black Temple...
Only to find Maiev there with several other Wardens. She encases you in a crystal and ships you off to the Vault of the Wardens. You "several years" (nine, real-time) in stasis, until Maiev breaks you out, throws you a new set of Glaives (you actually don't get to keep the original ones. I'll have to check that for transmog) and sets you off on the path to help break out your fellow Illidari.
You're then introduced to the conflict between Altruis the Sufferer (who was actually a quest-giver in BC that sent you after the Illidari) and Kayn Sunfury. The former broke off with Illidan because he felt the Betrayer had gone a little nuts and was acting too much like an actual demon, while the latter is fiercely loyal to the master. And one's a Night Elf and the other a Blood Elf, if that makes a difference to you.
Gul'dan and Cordana manage to steal Illidan's body, which cannot be good.
You fight your way through the literal dungeon, actually putting some of the bosses back in stasis while the demons pour out of their prisons, and eventually have to choose between either Kayn or Altruis to be your second-in-command, with the other going off on their own (I went with Altruis. I like to think that my guy wants to keep himself honest, and having a lieutenant who is willing to stand up to him is good for that. We'll have to see what the long-term effects of this choice are.)
Finally, you face the Eredar leader of the assault, after which you meet up with Khadgar, who brings you to your capital and then the quests begin to sync up with what the other players experience with demons attacking the leadership of your faction.
My computer is so ancient that it's hard to get a real feel for the flow of the class, but so far I really like the aesthetic (except the helmet I currently have - you get a second set of quest rewards in the vault that have a different look, but my older one upgraded to epic, so I'll have to take a trip to the transmogrifier.)
Anyway, DEMON HUNTERS ARE LIVE!
I can't wait to start doing all the other launch event stuff, but I think a lot of that will wait until I'm back home and can use my main computer.