This will definitely be an interesting debate.
I guess it depends on what your expectations have been for him. Coming out of UMASS and being the 2nd overall pick, the expectations were quite high for Camby. IMO, I thought he underachieved in Toronto. In my own eyes, I thought he could've been better than he was. He had a great playoff run for the Knicks in '99 and was a huge part of why they even made it to the Finals. Besides that Finals run, I'd say his days were mediocre.
You also start having to point at his injury troubles when discussing his career. Look at the early part of this decade, Camby only played in 29 games in back to back seasons. I think, at that point, a lot of people wrote off Camby. I certainly didn't anticipate him going on for another 6 years and counting.
My expectations for him have definitely been toned down for the better part of his days in Denver. This is when I think he developed a bit of a rejuvenation. He's stayed on the floor more consistently and turned into a great defender and rebounder. At this point, though, he's a roleplayer and as long as he's that, I think he's doing fine.
So I guess to answer the question, in the early part of his career Camby underachieved in my eyes. In the latter part of his career, my expectations for him dropped and he's seemed to take on the persona of a solid roleplayer. In that aspect, if he's healthy, he's meeting my expectations. I don't see him being overrated, perhaps, slightly underrated.