1UP has posted a discussion with Diablo game director Jay Wilson on, among other things, combat, character creation and class differentiation. It is as follows:

1UP: Someone could look at the new classes and make reductionist statements that compare them to the Diablo 2 classes. For those who claim the Wizard is just a reskinned Sorceress and that Witch Doctor is just a new name for Necromancer, what attributes would you point to that make these new classes different and not rehashes?

Jay Wilson: Well, for the Wizard versus the Sorceress, I would say that if someone makes the argument that the Wizard is just a reskinned Sorceress, I would respond, “Yeah, you’re right; the Wizard is basically a reskinned Sorceress.” What we couldn’t do with the Sorceress very well was break into what I’d call the old-school pen-and-paper magic user. You know the old magic user who could do a variety of things, like conjure up animals out of midair or create clouds of fog and acid or control time or disintegrate things or use death spells. They had this wide variety of magic that they could use compared to the more traditional elementalist — which is what the Sorceress is, meaning fire, ice, and lightning — who was just more limited. What we really wanted to do is break into this area, while if we just did the Sorceress again, we’d be like, “OK, you have to do fire, ice, and lightning, but where does disintegrate fit? Where does slow time fit in?” So we decided [that we'd] just take the same class mechanics, and [that we'd] change the basic concept and name and just have a throwback to that old-school magic user to give ourselves a broader range of magic skills. But there was never a huge desire to go away from the basic gameplay of the Sorceress; there’s a lot of repeated skills, and that’s intentional.

With the Witch Doctor, I’d say that the Witch Doctor is not a reskinned Necromancer. He has similarities, but I would say no more so than the Hunter and Warlock do in World of WarCraft. Sure, they’re both pet classes, but they don’t operate the same. For the Witch Doctor, we wanted to create a class whose pets were not his primary source of damage output. Sure, you can build a Necromancer that’s not reliant on pets, but most Necromancer builds are very pet heavy. The pets do a lot of the damage, and a lot of mechanics are built around debuffing the enemy so your pets can be better against them or taking advantage of the bodies your pets create by blowing them up with corpse explosion.

And on the progress of the classes in development:

1UP: Can you talk about the state of the classes? For example, is every class — even the two that you have yet to reveal — playable in the game right now?

 Jay Wilson: No. The fourth class is playable in game but is using a placeholder model — one of an NPC, actually. And all of the skills are what we call “programmer art” because we haven’t implemented actual skill effects. So that one is just in gameplay testing for us while we determine signature skills. The fifth class, we’re just about finished concepting it and are about to start building it. We can’t use placeholder art, so we’re now just going to build a model and start working on the first series of skills for that one. We’re actually spending more time on the Witch Doctor, Wizard, and Barbarian because of a big change we made to the skill system that we wanted to [integrate them] with — so it’s mostly just artwork that’s going on for the other two classes.

You can read the entire interview here.