I really hate that the Premium currency that you earn through the game isn't redistributable at all like other games or that you don't at least get a warning that if you spend it, it can't be used to get one of the more efficient permanent upgrades.
Warrior is pretty much Boss/Tank killer when Fury comes around. In normal fights, Stun pretty much locks down whoever is or is going to be a problem. Shaman is a handy all around. He can take hits, he can heal, he can do magic damage (consistent ~1.3k w/ Totem), he can do a little Phys damage on the side too. Very easy game.