Don't get me wrong I love Paizo books, I love their work, and I'm proud to own almost all of their publications.
However, Ultimate Intrigue is the one book I regret buying. It's even more than that, it's the one book i regret they ever published.
We need rules and systems, ok. We need a magic system because magic isn't a real thing. We need a combat system otherwise playing with your grilfriend become home abuse. But we don't need a social system because it's a ROLEPLAYING game. Either you want intrigue heavy campaign and you roleplay them, or you want to dungeon crawl or investigate (that's fine too) and you don't play intrigues. You can even do both and it's great.
Aside from that massive problem, the book suffers from "a turn normal actions into feats/class ability" syndrome. I can't count the number of time where players made me fighters to wizards or rogues with a dual identity. We didn't need the Vigilante, and still don't. And I loved when wizard use to get clever and ask for linguistics/bluff roll to blend a spell into a phrase. Now you need a feat for it. Thanks, Ultimate Intrigue. If that was not enough, some of these nonsense feat are built in feat tax chains.
But the one thing I hate the most about this book is the stupid FAQ it bestowed upon us to promote itself (https://paizo.com/paizo/faq/v5748nruor1fm#v5748eaic9tza). That makes a whole school of magic (illusion) utterly useless, and destroys a lot of others (enchantment).
Now I know I can just refuse to use it. But i use to love pathfinder for the clarity and perfect sense with out need to houserule much.