I finished the second (of four, initially--two more coming later this month after the release date hits) of the Paizo books that I got from Amazon, Lost Kingdoms. Unlike the first one I just reviewed, Blood of Fiends, this is the longer Pathfinder Campaign Setting series, which are 64-page softbacks with a squared spine that replaced the older Pathfinder Chronicles series of the same format. I also picked up, many months ago, the Lost Cities of Golarion, which is an interesting companion piece to this. I believe there's a third called Lost Dungeons or something like that, but since I avoid dungeoncrawls, I didn't pick it up.
Lost Kingdoms is a bit more "big picture"; although it refers to adventure locations, it usually does so somewhat obliquely, and without a lot of detail. In this regard, it's much like one of the region books--except that the lost kingdoms, of course, overlap existing regions.
For each of the six lost kingdoms mentioned, there is a map of what it used to look like, complete with some interesting points of reference or interest. There's a history of the kingdom, including what caused it to become lost or fallen. There's some detail on some treasure or antiquities that antiquarians may find in the ruins of the lost kingdom, as well as hazards left over as a legacy from them. Although it certainly felt geared towards the whole D&D dungeoncrawling experience (not surprising), because of its nature, its still certainly usable and interesting to those who eschew that paradigm as well.
However... there's also a feeling of deja vu for much of the book. The first section is ancient Osirion, for example. Waitaminute... don't I already have a book specifically on Osirion? And isn't one of the capitals of ancient Osirion part of the Lost Cities book? Well, they manage to talk about different details about ancient Osirion, but it does still, like I said, have a feel of deja vu. This is also true of the last entry, Thasillon, which has had so much coverage in several adventure paths, lots of stand-alone modules, and tons of material from Paizo generally. In fact, Thassillon, which is supposed to have been gone for 10,000 years (a ridiculously long time, which is a problem endemic in fantasy; it's not "impressive" enough unless the years are hugely inflated, for some reason) is significantly better known than many current regions in Golarion.
The other regions, however--Sarkoris, the Jistka Imperium, Ghol-Gan, and the Lirgen and Yamasa duology, are not really well known at all. In fact, the Jistka Imperium was one that I don't even remember reading about before anywhere (although I'm sure I have.) In general, the sections were very interesting to read, useful as adventure seeds (although lacking in a lot of details), and they come with a few "goodies"--each section has a few magic items and unique, new monsters. Plus, the entire concept goes a long way towards establishing a sense of "depth" to the campaign setting, which is a good thing in its own right.