Defensively he is tough, his problem is that he provides zero offense. He can't shoot, can't drive, and doesn't pass well.
The weird thing is that he could shoot and drive his rookie year. He made some great moves and could use both hands in the key. And he was the Bulls only real outside threat during his rookie year.
I don't know what happened to him, but that rookie year he was my favorite Bull but last year I just saw myself swearing at the screen with a puzzled look when he missed shot after shot by 3 feet.