He's just too inconsistent to play in a top 4 midfield. A highlights reel player.
No doubt he's capable of absolute pearlers in terms of shots and his delivery, like the one to Carroll against Wolves or the shot that rattled the bar vs Everton. but we are talking about really low percentages, they just don't happen often enough and when they don't it exposes every other flaw in his game.
And those flaws can be ugly. He's a horrific tackler of the ball, if you can even call it that. Positional sense is poor and the main one for me is that he's far too selfish a player, and thats one of my fucking pet hates. Countless times he's had the option to square passes to people in much better positions (Wolves, Fulham, Everton, Villa, etc )
but time and time again he tries to barge through 3 players and just bumbles into a heap, or takes a shot himself. Every time he does it it just notches him further and further down in my estimations as a player.
No doubt with that, you could cobble together a 6 minute video at the end of the season with some beautiful raking passes and some whipped crosses, shots etc, but we are talking about doing it over a potential 4000 minutes over 38 + games, which brings it into perspective a bit.
To compound his selfishness I just don't think he has the game intelligence. He's not smart enough to be a playmaker who can detect the tempo of a game, slow it down and keep possession, quicken it up and go for the kill etc, and its what separates truly great players like Xabi with your Charlie Adams of this world.