He was overrated the same way the NBA overrates players by basing a ranking or value based on athletic skills and potential.  He has very little offensive game other than dunks and put backs.  Never developed a reliable go to shot - short hook, turn around jumper from 5-10' or anything from the post position.  If you don't have that and you don't have an outside shot or good enough ball handling ability to drive (which he also lacks) you are easy to stop.  Add in the fact that his free throw efforts were frighteningly erratic and often bad and you get a player who is mostly a liability on the offensive end. 

He gets pushed around in the post way too easy and seemed to rely on his length to try and block shots rather than maintaining good defensive position.  He did intimidate some drives, but he could be backed down by bulkier players way too easily to be a stalwart defender. 

He needed to work very hard at his game at both ends of the court and in the weight room. I suspect he thought he was working hard because he was going harder than he did in HS, but not hard enough to translate his admittedly top notch physical skills - quickness, length, jumping ability - into being a quality basketball player. I have seen Pelphrey coach some very raw players into quality big men, so I think a good bit of the lack of production is on Walker and not the coaching staff.

I'm sorry it didn't work out for him at UF, but as far as the team goes he wasn't contributing too much and the stats he did compile should be fairly easy to make up.