I started with a barbarian and it's been a total blast. There's just something satisfying about getting surrounded by 20+ monsters, slamming the ground and stunning all of them, then sending out a shock wave across half the screen that obliterates nearly all of them into a cloud of monster parts. I don't like gore, but it's pretty satisfying.
Oh, and the game is gorgeous. I started Act II over the weekend, which is in a desert. You can't really tell from this screenshot but there is a constant flow of sand moving around on screen here. And it looks amazing, even with my 6 year old Dell (but I did put a decent video card in it a few years ago). My barbarian is below (as of 5/21).