Despite having just about every sort of region, including many based on our own historical earth (but with, like, magic), the potential (and in the case of regions covered by APs so far, actual) depth within each region means that, in effect, you can have just about any sort of campaign you want. Also, it's relatively well-written** and cared for by the people that did (in my opinion) an excellent job in shepherding Greyhawk when they had Dungeon and Dragon. You want Gothic Horror, Oriental, South Asian, megalopolis, ancient Egypt, Expedition to the Barrier Peaks-style buried and not-understood technology, wild and untamed/PoL, Arabian Nights, decaying once-mighty empire, devil-worshipping aristo tyrants, chaotic revolutionary France, endless steppes, perpetual crusade, a cult of atheism, jungles full of lost civilisations, evil empire under the waves, Atlantis, a permanent hurricane, etc, you can find it in Golarion. I should be clear that magic may have to be used to explain how all this stuff can exist...
It's also by Paizo, which for me is an excellent indication of quality.
*But not outstanding, I fear. Some Gygaxian prose and the Campaign Guide has a foreword by Bob Salvatore, surely the World's Worst Living Author, which raises mostly unjustified fears that the book might be similar to Savatore's work.
EDIT: In addition to the Dungeon/Dragon team, there's now SKR as well, who did great stuff on Greyhawk when he was at WotC.