Personally, I think the two biggest areas of his game he needs to try and improve in are his technical ability and finishing.
Physically, he's pretty much there. Not only is he a hard worker, but he's also strong and can battle for most balls, and he can also hold players off as well which comes in handy.
He's shown glimpses of technical ability, however I do think that it's an area he has to work in as he often looks rather clumbsy when he's running with the ball.
He is a decent finisher, and it's not his finishing in itself that it is the problem, it's often the type of shot he chooses to go for. There's been many an occasion where it's been best for him just to put his foot through it and go for it, however he's decided to go for the finesse shot instead. That can be rather frustrating at times.