It's pretty much impossible to describe all the goodness of this product in a short review—or even a long one. I have never seen any campaign setting--much less one that's really just a single city--presented with such great care and thoroughness. If you're looking for a new setting for a 3.5e d20/OGL campaign, and you're interested in urban adventures, look no further. From the gazetteer to prestige classes to new spells and monsters, this product offers incredibly rich play experiences. Malhavoc also publishes several adventures for the setting, and SkeletonKey Games offers a poster map of the city (well, if you assemble it as such after printing) and miniatures-scale map tiles especially for Ptolus. I would still be running my Ptolus campaign if I hadn't upgraded to 4e (converting or recreating Ptolus in 4e stats was far too daunting a task)--and if I ever go back to 3.5e, I'll also go back to Ptolus.
[5 of 5 Stars!]