Because he has great size, athletisim, pretty form on his jump shot, and can defend, in spurts, at an incredible level. Not to mention a lot of those players were not near as raw as George coming out of college. I didn't expect him to even play much this year.
The reason I think he can be a top player is because of his insane body control. He is absurdly smooth in his motions which took me by surprise when I first saw him. When you consider that he has only been playing the wing position for 3 years now his smoothness is even more impressive.
He was playing incredibly well when he was the man to score off the bench. I really hate that he's stuck with the starters because none of them, besides Roy, are good passers. I think he could put up 10-15 a game if he was given more chances to score and stopped shooting spot up threes so much.