This book helps clear up and collect a lot of older material, balanced now with other released material for GMs. It also adds in a wealth of new material for factions of Adventurers across Golarion.
A solid collection of old and new under one singular heading.
Some factions contain major spoilers, making it hard for a GM to just pass off to players who may be playing certain APs.
Inclusion of multiple races and creeds and even transgendered factions and npcs in multiple parts of the book. This book really fleshed out some factions which had little to no crunch.
Certain feats are fun but others are less the useable. A feat that allows a bonus on maneuvers but doesn't stack with improved maneuver feats? Those are the ones that help avoid AoO. So what's the point of the feat? Additionally a heads up to some people about the amount of reprints would have calmed an angry section of customers.
Honestly I love the book and can't wait to try out some of the new material and some of the updated versions of older (and due to other books options more unbalanced) options.
When you get past the salty tears of angry optimizers, you're left with a fine entry into the guides section with Inner Seas flavour.