He reminds me of Anthony Randolph. IF he has reliable mid range shot and a brain then he'll excel in the NBA. He relies a lot on dunks though, and once he gets to the NBA he'll be going against the best big men around the world who won't allow any dunking.
I should've been more specific, but I'm comparing them in terms of athletism and height. Both players are rare cases of big, fast and athletic big men, which is why Griffin reminds me of him. This is also why I specifically mentioned Griffin having a brain,as well because Randolph's IQ is below that of an average player obviously. Though Randolph is a stickman in my opinion, whiles Griffin appears to already be a well-built, athletic, big man, with a prepared brain, which is very rare.
I think he'll end up putting up Duncan-like numbers. Slightly less than Duncan has averaged throughout his career, but somewhat similar. For his rookie year stats: 18 Points Per Game 9.5 Rebounds per game