The key problem with him is he has a poor shooting percentage and bad shot selection. Personally I think he is a good shooter (Despite his percentages), who can penetrate and dish and is underrated. Syracuse has never really had another guy who can create his own shot since Melo left. I realize that Warrick and Devendorf were decent at it, but all of the pressure seemed to be on G-Mac to create for his team. And he did create for his team, he just wasn't good enough to create for weak teams and score effeciently at the same time.
He is one of these guys who has a role in the NBA it just isn't necessarily going to be a big role or a particularly glamorous one. Backup point gaurd for a team like Miami, in there to hit big shots and pass the ball to Shaq/Wade in the right place.