It was interesting watching Kessler last night on the defensive end. He is super disciplined in boxing out for rebounds and not over defending jump shooters. As soon as a shot would leave the offensive player's hands he immediately would get in position for a rebound. Right now I think his best attributes are his understanding and feel for the game. It's funny that he looks like Hardy, since they seem to have a lot of the same qualities.
As far as upside, I'm really not sure. Since he isn't overly athletic or seems to have a lot of potential as a shooter, he probably never makes an all star team or anything like that.