The Witchdoctor is shit. Well not complete shit, but the skills they showed in the trailer were all old, except the "Swarm" thing or whatever it was called, but that basically just some kind of chain lightning.
The dungeon system looks boring, just like D2. Random areas are nice but a REAL world is much better.
5 different classes are ok, or at least I thought so. If they put 3 old classes in the remaining 3 open slots, D3 is just like D2 but with better graphics. They need at least Sorc, Paladin, Amazon and one new class in addition to the Barbarian and the Witchdoctor, I hope the add more new classes with an add-on later. I never really played with a Necro but if they leave him out it's for sure that the Witchdoctor is the Necro 2.0 (summoning, curses, poison)
The events looked all scripted (the thing with the rocks destroying the brige was crap).
tl;dr I'll definally buy D3, it's going to be awesome.