My goodness, where to begin? Well, I suppose I'll start off by saying that in every game of this type, I play a mage or similar caster 99.9% of the time. So I freaking LOVE mages. What am I excited about? Well, here we go. Most of this is from Peter Thomas' thread, but not all.
1.) Better robes.
2.) Cool spells, both old and new. I realize some have been cut, but I think that there were a lot that could have been eliminated and/or consolidated into other spells since we have the upgrade system now.
3.) I'm psyched for better differentiation between the elemental categories of spells. According to Thomas, Fire deals the most damage over the widest area, Cold slows and stops enemies over the smallest area with shorter range, Earth has high impact strength, and lightning deals moderate damage over areas (though not as big as fire), ignores friendly fire, is very fast, and has the potential to stun. I'm excited about this because in Origins all of the primal spells felt very repetitive to me.
4.) Mages can now attack at melee range with their basic attack, which makes more sense to me. It should be noted in case anyone missed it, that this is the same damage as their pew pew pew attack (though that is now a bit different I believe). So they still aren't warriors.
5.) Mages have finishing moves.
6.) They still have healing and CC abilities, though we don't know to what extent (I'm not worried).
7.) Spells will no longer overlap as much as they did in Origins; they are more unique to themselves.
8.) Spells can be upgraded, allowing you to increase the effectiveness of certain spells that you like. They're trying to make this roughly equivalent to getting a brand new ability (a made-up example he used was upgrading a single-target spell so that it explodes and damages nearby enemies instead of just one).
9.) Animations. We received an example from Thomas about a mage slamming her staff into the ground as a finisher and sending a wave of fire into an enemy or something like that. He also stated that as far as what they do to cast and stuff is much more visually interesting and I'm really excited. There were really only (with the staff equipped) three different animations in Origins.