Well, first I would say that he's not past it yet. He could go on to have many fine seasons yet - but, again, I think that depends on whether he stays with us.
Secondly, I'd say he hasn't lived up to the enormous expectations people had when he first came into the limelight as a teenager. I remember thinking we had signed a latter-day Charlton when he arrived from Everton. He hasn't turned out quite as spectacular, that's a fact.
Thirdly, whether he has lived up to his potential (rather than people's expectations) is hard to tell. As I've said before in this thread I've come to regard him as a bit of an oddball - as a player. Someone who doesn't quite fit any category, perhaps. And in many ways I think he has always been such a player. The enormous, raw talent that some say he has - at least partially wasted - probably wasn't quite there to begin with. And by that I don't mean to imply he lacked raw talent - just that he didn't possess it to the same extent as a Best, Maradona or Messi. He didn't have that genius-like effortlessness to his game that such players seem to come with.
In terms of living up to his talent I'd say, then, that he is there or thereabouts. But the main thing is - and this is why I don't want him gone - I actually think he hasn't played out his register yet. I think he can become an even better player; that he can become more consistent, more focused, finally shed that last layer of immaturity which hampers his game a little too often.
And if that happens at some other club - well, then I'd call that a fecking waste. For us.