As good as he wants to be. The only thing that can stop him is himself. A super talent. Why Fergie cleared him off rather than just loaning him out god only knows especially after he himself said he is the best Midfielder since Paul Scholes
Apparently Ravel knew too many bad people in & around Manchester and Fergie decided, for Ravel's own good, that he had to move totally away from Manchester.
Also, again apparently, there's a clause in his contract that gives United first option if Ravel ever moves from West Ham.
Slime.
He can be awesome. Him and Paul Pogba have enormous potential. However, they both fell foul of greedy agents (maybe themselves aswell) and if you believe what you read, they were asking for huge amounts of money. Same thing happened with Sturridge when he left City.