He's looking really good. The biggest criticism of him in Germany was that he switched off alot and got sloppy with his play when he did. I think the worst example of that we've only really witnessed when he's been out of position and up against a player like Hazard (who most would struggle against), so that bodes well as far as his concentration goes.
As said, I think he'll come into his own when he builds up the fitness to play in central midfield every week. When he goes on those runs forward, he's great at dropping his shoulder and finding a pass, if we can just fine tune his game a touch, he'll start to get amongst the goals and assists, because he's too technically gifted not to.