As described, the book contains two main parts, one about creating factions, the other part is a collection of different factions which can be used for your own game or adapted to fit into your world.
The first part is very well written and in my opinion illustrates perfectly what you have to keep in mind when creating factions - or even WHY you should create factions - in your game. This part alone is already enough to build whatever you want to have in your world and helps greatly in planning the faction, be it a guild, a group of mercenaries or a religious order, and in what you have to think about to when fleshing it out.
The second part of the book is a collection of amazingly well written factions, all of which can be used almost instantly or at least adapted to fit into your game. They fit best into fantasy campaigns and stories but can be easily used in any other genre if you change just a few things, if at all. The factions are unique and use very interesting ideas.
Having a lot of details makes all of them all the more vivid and "real" and if you think about what they are and what they want to do you'll see that every one of them provides a ton of material to work with in your game. If nothing else they're an excellent source of inspiration for creating something yourself and using the tips and guidelines you can quickly create your very own faction specifically for whatever you need in your game, even if it does seem overwhelming at first.
In my opinion it's an amazing book for new and old GMs alike to use in your game if you plan on introducing groups and factions.
[5 of 5 Stars!]