I agree to a point, but you've got to at least do the basics and he hasn't.
I've made the point before that the chopping and changing might mean you occasionally look a fool because you thought your partner was going to do something that they don't do, or you don't trust your full back so you go haring out to do something you'd never normally do, that's fine. What chopping and changing doesn't do though, is make you lose the ability to mark your man, or mean that your legs go to jelly every time a player runs at you, or prevent you from having the bravery to put your body in where it hurts, or from passing the ball to your team mates. Keane has struggled with each and every one of those things this season though. I thought he'd be a good signing, and for the first few months of the season I was saying the same thing - that he'd come good and be fine in the right unit - but the more I've seen of him, the less I believe that to be the case. I'm not totally writing him off, but I honestly think he's got a long way to go to even suggest that he's a decent squad player nevermind that we should be relying on him as a mainstay for the next 5 years.
You're right about the bipolar thing, but the issue is actually the praise not the criticism. The truth is, on Wednesday he was only about a 7/10, maybe an 8 at a push, but because it was the best he'd played for ages we all came out and said how well he'd done and it was great that he was finally getting there. 3 days later he's back to the 4 or 5 out of 10 that we're used to and people will obviously comment on that.