Well-balanced
I haven't played one or had one run in a game I was DM-ing, but it doesn't seem to be an overpowered class. A cleric taking it gives up a good deal. The contemplative has slower BAB progression, poorer saves, no advancement in undead turning, lower hp, etc. Sure, the prestige domains and the divine wholeness/soul/body abilities are nice, but it's nowhere close to gamebreaking. The PrC might actually be a leg up for a wizard, but I'd personally require very strong roleplaying reasons before giving a wizard access to it. Also remember that this is a PrC that isn't available before 11th lvl (you need to be 10th to meet the requirements), so it is understandable if it were more powerful than many other PrCs out there, but I don't think it is.