They said some of it is going to be randomly generated.
The FAQ says 5 characters and a male/female option. Other than that, I'm assuming the classes will be better balanced so there are no classes that are only good with a party, if that. (I'm looking at YOU, Paladin.) I also think the only customization we're getting is visual equipment, but I'm fine with that.
They said they wanted a fresh start, so I think they're only going to include a maximum of one more old class.
They said it's going to be a similar length to D2, which would suck, because I can beat the game super fast. I also think they're having acts, if I recall correctly, they said they are during an interview.
HOPEFULLY, the skill system will be similar.