I like Tatum's potential on both ends and also on the boards.
I think his defense is very underrated, and that he has a chance to be very good on that end. He has long arms, a wide upper body to guard bigger guys eventually, quick hands, plays the passing lanes well, and is a high-IQ guy.
If his offense can become more efficient (which it will under Brad Stevens), he gets more consistent from three, and starts passing a little bit, he will be a star in this league.