I'm excited.  The new Death Knight class sounds pretty cool.  I like the idea of a rune-based casting system as opposed to mana/rage/energy.  Plus once you do the DK quest you can instantly create a level 55 char on any server :)

I have to say though, this expansion sounds like it will have significantly fewer goodies than TBC.  TBC introduced flying mounts and 2 new races.  with WotLK we get DK and...new hairstyles...?

Still, psyched about the DK though.