I have little idea how WoW plays (I can't stand it; too many bad experiences invlving friends) soI can' thelp with that criteria but: Dungeon Fighter Online.
2D sidescrolling beat-em-up goodness, 25 classes of characters each with their own special moves. Its nature makes it easier to pick up than most MMOs. Been meaning to give it its own thread for a while, now.
It's based on the Korean free-to-play model, so while everything gameplay-related is free, expect to break open the paypal account if you want your character wearing something besides their generic outfit.