Wizards and witch doctors will be really gimped in group play. They rely on auto-target long range attacks to win. How dumb would it be for a haunted enemy to die then pass the haunt to your teammate and have him die? It's absurd. Wizards are weak enough as it is, nobody is going to want to play with one. Storm armor is basically the only thing making them semi-viable as it is.
It'll just be a barb/monk/dh fest.