This is a somewhat strange campaign setting book, in the sense it seems not only is the various regions described in the book very different (from very regular fantasy tropes and/or very real world inspired) to the very fantastic... But how they are described also varies so much, because the authors do their pieces in very different ways.
For example, one region might have a city statblock, a lot of info on people there that can be usefull and inspiring, written in an entertaining way... While at least one other is pretty much "there are these guys guarding something but I won't tell you much about either" over three pages.
I found some of the articles in the book excellent, some average and some bad. As there is something to every taste here (except crunch, this is pretty much pure fluff), I guess that would be true for most people too.
Stolen Lands takes the Sandbox type of game, and it's very essence seeps into the book itself.
Which is a mixed blessing. The adventure itself doesn't have a great story per se, but the various encounters can end up being far more entertaining than what a tight story might have been. The Brevoy article is superb, the short story is funny in a Monty Python kind of way and the monsters are somewhat interesting. And the hexploration article works.
However, the layout is very annoying. XP/rewards are all over the place, and often hidden in big block of text in another place. The hexploration article only have "sortof" rules that feels lacking (perhaps it was cut a bit?) for being useful outside the module except for travel times. In other words, be awake when reading and keep post it notes on hand. Which feels a bit weird, since layout in these books tends to be good.
After GMing this (pathfinderizing it first -using the Fast Track progress and upgrading all the encounters so the CR is right), I found it to be one of the more entertaining modules I've run.
The best part of it is the start; using the player's guide gives the characters lots of motivation for starting the whole thing - so it's a lot of caring in the first section. After that, the main story ends up being pretty much a typical "I do it for the gold" thing. What makes it good is all the barely mentioned NPCs, the interesting tidbits that ends up happening outside the main story and so on.
The fiction bit I forgot 5 minutes after reading it, the Harrowing section is kinda wasted space if you have the Harrow Deck, and the Varisian article is decent, but feels more like an appetizer than anything else.
As far as setting overview books go, this is the best one yet for anywhere, in my opinion.
Most of all, the diverse amount of countries (and their own in a way crashing flavors) is bound together in a very organic way. I might not really enjoy having the Mana Wastes, Cheliax and Numeria show up in the same world - but here it works.
Art is amazing, every country section is inspiring in it's own way, it's well written and it's pretty much a must have if you play in Golarion. I've tried to find a fault with it, but I really can't...
This folio has overview maps of Ustalav and some of the settlements the Carrion Crown AP takes place in... It is mostly useful if you like to give player's a sense of scale. No tactical maps of any scale is included, so no combat shortcuts.
The big map of the Ustalav itself is very good. However, I'd really like to see at least a couple of major roads marked... As it is, the whole place looks just like one big wilderness.
The other maps are also good and evocative. But I'd rather see all of the settlements in the AP get represented, instead of just a selection of them.
So all in all, it ends up being just sort of helpful.