Fantastic rules if you want to make Pathfinder even more in-depth, but the true gem of the book is the amazingly fun Kingdom Building rules from the Kingmaker campaign path. Whilst a little unwieldy to use, it was an incredible experience building up a kingdom from scratch. This book is worth it for those rules alone.
This is one of the best books one can buy for Pathfinder (Beyond the necessary Players guide and bestiary, of course.) I have found the advice of this book to be very helpful in designing not only PC's, but also NPC's, quests, kingdoms etc. Recommended for anyone who thinks they need help in designing a world in which they or their players can adventure.
I love this book, I Also loved the Gamemastery guide
Anyone looking to flesh out a campaign world will find lots of useful stuff in here. I like the rules on kingdom building a lot and the down time rules for POCs building inns, shops, taverns, keeps, guilds, magic towers etc are great
The Ultimate Campaign book is a good solid Pathfinder source book.
The character background chapter is useful for both players looking to flesh out their characters, and for GM's looking to develop NPC's and looking to integrate the players background into game play. It's nothing ground breaking, but it's a useful chapter to have for everyone to benefit from, player or GM.
The rest of the book is chock full of useful material, such as the 'downtime' chapter that helps flesh out what the players can get up to when they aren't out adventuring. Sure, none of this is necessarily new or earth shattering rules and guidance, and most GM's have just been making this stuff up as they went along, but it's nice to have it written down and codified into something that everyone can then develop their ideas from. There is an interesting section on Alignments that talks about incremental alignment change, and a reasonable section on bargaining (the commodities variety, not the infernal!), and the later chapters on kingdom building and mass combat seem to be competent, if not necessarily inspired.
All in all, it's a very solid 4.5 out of 5, but as they don't do .5 stars, I'll have to give it a 5 star rating. Definitely worth buying if you like getting into the background and nitty gritty of your campaign world.