As they say, if you're going to gamble, you gamble on bigs. (happens almost every year, almost every year they're busts...) :)
I think this guy happens to have a really nice feel - moves very fluid.
Thinking back to Pau Gasol (#3 overall pick), I remember watching an early game with him on TnT or vs the Knicks and thinking - damn, what a waste of a pick when I first saw him. Then he went to work and put up numbers. He had a fantastic rookie season. He'll be part of the basketball hall of fame one day and will always be in the debate for best foreign basketball player in the history of the game.
Rookie stats, age 21: 17.6ppg, 8.9rpg, 2.7apg, 2.1bpg, 51.8FG%.
As far as thin is concerned - some guys just have it. Some guys are always going to look rail thin - as long as they're comfortable with their bodies, go with it.
K Mart (at age 45 with the Knicks) looked almost exactly the same as his rookie year with the Nets. Kevin Durant is still rail thin. So is Tyson Chandler (especially his legs).
You can't expect these lean guys to hulk out and be something they're not - you hope he's the type of guy that can use his height to his advantage and be one of those guys that can be slippery to get position.
Beautiful outside shot, solid footwork. What will make or break him is his ability to see the floor (basketball IQ). What you need to look for is whether he can make the smart pass and be capable of average 2-3apg from the get-go... and also shoot ~50% from the field. That's what the triangle system needs. If he can't do those things, he's not going to be a good fit.