There are differences:
Special move is unique plus (I can't find this post) a wizard gets more mana from intelligence, for example and there are damage differences. Search the forums and you'll find this post, it's by Raze.
As for the classes:
RPGDot: Is there the same selection again of Warrior, Wizard, Survivor? And if so do they have the same special move?
Lar: No. This time it’s totally generic. And contrary to Divinity 1, all characters can now sneak and execute whirlwind attacks. It’s not limited to specific classes anymore.
It was mentioned in the interview.
