I feel like DK is a mage/rogue/paladin mix because:
self-healing is based off melee, so it's like paladin melee + art of war
the dots are pretty trivial to manage and tied to direct damage skills, so it feels more like fireball's dot or flame shock
runic power feels like energy even though it builds like rage
blood talents and D&D feel like a combination of paladin ret/prot talents and consecrate
quickly spamming skills feels like rogue gameplay (probably why a lot of rogues went DK early on?)
This is coming from someone who's played everything but rogue, druid, warlock and hunter to northrend levels. I played warlock a lot back in the day, but quit it before TBC and now I main a paladin to tank and have a shaman healer alt and warrior alt just because I like arms' gameplay style. Or I did anyway, but I haven't even finished getting my warrior to 80 and I quit before the bladestorm disarm nerf. Anyway, in lore they definitely try to make DKs feel like a mix of warrior and warlock, but in gameplay they feel like evil paladins with a little bit of mage and rogue to me.
Personally, in the expansion I'm going to try goblin warlock/hunter in beta, and if I like hunter more, I will play hunter in retail. If I don't, I'll give warlock a shot, although I might stick with making an orc warlock alt to experience "old" world stuff starting in durotar. If I don't like goblin warlock, I'll do goblin mage, since mages sound like the new hero class with all the stuff they get. But I'm actually mostly interested in seeing how the changes affect hunters and if I wind up liking them more than I do now.
Worgen still seems like the lamest race ever, though. It's like they decided they had a zone, but couldn't change it so the people living there weren't human, so they came up with a werewolf curse so it's not just Elwynn Forest 2.0.