"In this world, massive cities line the coasts of an inland sea, the last refuge of the world's living things in the wake of a cataclysm that has gripped the extreme latitudes in an Ice Age, and parched the rest of the land into a vast desert."
The above would pretty adequately sum up my campaign setting's geography, so you can probably see why theoretically, every one of these books would be of some use to me. However, it has been my experience that my Players will do anything and everything in their power to stay away from glaciers, deserts, oceans, or major cities. While I own a copy of Sandstorm, and for a while had access to a friend with Frostburn, the PCs steadfastly avoided any contact with the extreme areas of the globe. The only one of these environs they visited was the sea, since there was no other means of travel available, and I had already bought the Seafarer's Handbook long before even the first environment book had been released. I've looked over Stormwrack, and while overall the book looks to be of decent quality, I feel like it would not give me much that the Seafarer's handbook hasn't already given me. Moreover, since Stormwrack assumes a purely Dark Age level of technology, and I simply don't have any interest in sea travel before the age of Blackpowder canons and flintlocks (which my campaign has), it doesn't seem to offer me much in the way of usable content besides monsters and some equipment.
That said, I'm currently running an Urban Game set in my homebrew's largest city, so I've been looking for a book that would help me flesh out cities. Today I looked at Cityscape, Cityworks, Ptolus, and Five Fingers: Port of Intrigue, and of the four, I think that Cityscape might be the weakest, even considering that two of them are campaign specific! I'll probably end up picking up CityWorks (to complement The SeaFarer's Handbook and Sorcery & Steam) and maybe Ptolus if I can scrape together the money.
Robert "Third Party Material Just Seems To Work Better For Me" Ranting