Who is over-rating him? I knew from the day he was drafted at #1 that he was going to struggle to live up to the enormous expectations that come with that status. That doesn't mean that he is a bust though.
He has improved his rebounding numbers every season. Last season, at 10.3 per game, he was the 5th best rebounding centre in the game. Only Howard, Biedrins, Camby and Jefferson were ahead of him. He also shoots a good percentage from the field and is still recognised as a good passer for a big man.
I'd rate Howard, Okafor and Perkins ahead of him in the East. Horford and Brooke Lopez are good prospects but I don't think are as good as Bogut yet. Ilgauskas is a clutch shooter, but I don't think he is as good overall. Wallace is on the slide and to me is not really a true centre anyway. In the West, clearly Biedrins, Jefferson and Yao are better. You could probably add Duncan and Pau Gasol too, as they play like centres to a large degree. Shaq is still just better as well, but won't be around much longer.
I'd say the main knocks on Bogut are really that he is not a standout either offensively or defensively, and that he is injury prone.
I still think his career could go either way. He has now missed 66 games in 3 seasons, 46 of which came last season. Next season it is critical that he stays injury free - both to counter the injury prone tag, and to have a chance to finish out a season strongly, instead of on the injured list.
The other things he needs to do are:
1) Get a good big man coach to work on his footwork and on developing a consistent hook shot. If you see what Clifford Ray has done for Perkins in Boston, you know that Bogut could improve vastly in this area with the right coaching.
2) Watch tons of video on how Perkins defends the post, because if he just improves his positioning on defence, he can improve his defence a lot as well.
3) Improve his conditioning - when I have watched him, I've noticed that he sometimes seems out of gas sooner than his opponent. When that happens, he gets a bit passive, and opponents get position on him too easily, and draw cheap fouls on him.
If he can at least do two of those three things and help lead the Bucks to the playoffs next year, he will be right back on track as one of the elite centres in the league IMO.