I played through the entire campaign as a sorcerer. Love the sorcerer. Didn't touch the other characters. Now I'm trying the others out. The barbarian isn't wowing me. But the necromancer is so much fun. I especially like the exploding corpses skill and the domino effect when the monsters keep advancing into already dead ones. I didn't think I would like necromancers, but they may be my next playthrough or the Season 1 character.
I am playing a barb as my first character. I leveled up as a rend/bleed/thorns barb which was okay but felt quite slow. I switched to whirlwind at level 50 and while I still have a long way to go to complete the build, it is already very effective at clearing as well as bossfights. That said, I am not sure yet as to what to play in Season 1. All classes are looking fun in their own ways.