He definitely hasn't been amazing. Not that I've seen much of him - 5 games or so, but he hasn't grabbed the headlines and doesn't have very good numbers either.
I don't doubt his talent for a second, the kid can do pretty much anything, but maybe his attitude should be called into question a little. His team are gunning for the title, and he should be 100% focussed on helping them achieve that. To me, it looks like he badly wants a big move away, and feels like he's wasting a year out of the limelight and away from the real top level football by staying at Lille. I don't worry too much about that though, if Wenger signed him it would be because he believes as much in is character as he does in his talent, and Wenger rarely gets it wrong on that front.