I think of him as a rich man's Varejao -- better defensively, faster, but offensively limited (have you seen his shot yet? haha), and rail thin. He's not a great athlete. I think he fits well with a team that's already a contender, so he's ok on the Bulls. I like him better than Hawes, who I think will be a bust.
I don't think his ceiling is high. He has gotten by on a lot of hustle, imo.
He will be the only person in the NBA to put a side spin on a ball when he shoots.