It seems this way to me, feel free to disagree/correct:
Wizard: DPS spellcaster/nuke.
Monk: Melee support/healer.
Demon Hunter: Ranged support/nuke.
Witchdoctor: Just kinda... there. I don't get it.
EDIT: For the record, I'm aware Diablo 3 is not played exactly like this. In fact it was Blizzard's intent to avoid this cliche. However, you can't deny the monk has the most spells with healing attributes. Period.
There are two main factors that bother me personally.
1) Skeletons. I miss summoning skeletons! If the WD could summon skeletons it would really bring the player back to the d2 days as a tribute to the necromancer. Almost like a "sorry fans for ditching the Necro, here's some skeletons for ya!".
2) Exploding frogs? Seriously, Blizzard thought that was a good idea? Does that sound at all like something that would destroy hordes of demons to anyone? It sounds more like one of Blizzard's april fools jokes. But it's reality.
And yes, I understand it's too late in development for any of these changes to be made. I posted this for that exact reason. Because there are still people out there like me that believe the witchdoctor ruins 1/5th of Diablo 3. However, the other 4/5ths are perfect so we're buying the game anyway.