Watching him vs Chelsea, you can see that he's the focal point for West Ham's attack and is very good at it. The quick touches & driving runs are coming off and makes one wonder where was this for the last few years. I think part of it is a sense of freedom, as any mistakes aren't as magnified if he was a United player. Plus as the main creator instead of just a cog on a better team, he HAS to do & try more. I doubt he would provide similar results for United as there are better players ahead of him along with bigger egos/presences for him to provide a similar boost. He needs to be the focal point to get the best out of him, but he couldn't be the one at United.