It depends on your definition of good. I had him down as "good" last season, this season not so much.
What is he worth to us? I'd want £6m myself based on that potential, but I would probably sell at that under the current circumstances.
We probably could get £6 - -£7m for him in this summers market, with players like Jelevic going for £6m+. He's young and other managers might think they can take him onto another level.
He seems to be one of those players that other teams think is better than he is aswell. We'd get £6m but i don't think what he gives you is worth more than £3m.
That's my opinion