This is really an excellent collection of superb NPCs for your Pathfinder (or 3.5) game! There are a lot of NPCs of varying level/CR and of lots of different types. I am using this book a lot in my current level 16-18 homebrew PF campaign, where I really cannot live without it (!!!). But it will be equally useful for any level-range of campaign.
The NPCs herein are both very solid builds crunch-wise (much superior to a certain 1st party NPC collection IMO), and they also have very good and thorough sections regarding their fluff, history and role. And on top of that they have very useful recommendations concerning their tactics in-game! I LOVE IT!
Most of the NPCs are very evocative and really sparks your imagination! Some of the NPCs - and groups of NPCs - in this book can almost singlehandedly inspire an entire campaign or adventure!
Together with Frog God Games, Raging Swan Press is now my number one favorite publisher for Pathfinder, bar none!
I wholeheartedly recommend this to GMs of ANY fantasy RPG! It is an excellent general-use GMs toolbox, both for preparing homebrew adventures, and for adding content to published adventures. It is also VERY useful while playing AT the table, where I use it a lot. To me it reminds me of the 1e AD&D DMG (all the charts at the back of the book), but Raging Swan Press' Dungeon Dressing book is just (to me) MUCH more directly useful, and it VERY well organized. Besides LOTS of random tables containing A LOT of solid and imaginative content, there is also a lot of very useful CRUNCH information in this book.
For ANY Pathfinder GM I really would consider this a mandatory GM's ressource. It is so good, that I personally consider it the number 1 "DMG" for Pathfinder! (I almost wish that Paizo got to publish it as an "Gamemastery Guide 2", so that more people would get it!)
TLDR: Get it if you are a Pathfinder/D&D/any fantasy RPG GM! You won't regret it, I am sure!!
PS: I can also REALLY recommend that you look at the Wilderness Dressing book and Scions of Evil (superb NPC collection), also from Raging Swan Press.