Soooo...I'm going to say that I obsessively collect Pathfinder products, and as such, much of this material is old hat for me. Emphasis here is 'for me.' With that said, I want to examine this in a vacuum.
The artwork is good, but then, it's been good. It serves more as a 'Faction Guide 2' for me than anything, giving some details about the various organizations, class options, feats, and ties. In particular, though, I like that I don't have to flip through two or three books to get character options for the factions. Hellknights in particular were always a pain due to how diffuse their rules were. I can now hand this book to a person and say "here ya go. Here's some ideas of factions in the setting."
One drawback, as has been mentioned, is spoilers for the various APs. While I use those sparingly, it can be somewhat problematic, and I'd suggest steering players away from this if that's the case.
Overall, it's a decent enough product. If you're new to the setting, it's worth picking up as a nice collected list. If you're old hat, a few options inside are interesting enough, and a few setting updates are worth examining. I'm particularly interested in the Lantern Bearers' new direction.
So Bestiary 5 was a bit disappointing to me, but this one is something that did something with Pathfinder I haven't seen in a while: gave me ideas that I wanted to use. A lot of the monsters presented are honestly interesting. As usual, there are some reprints from other products, but I always favor having consolidated lists of things. I won't use everything, but there is enough here that I'll be using a good chunk.
Also, the weremantis reminded me how much I love Portal, so I have to give it to them there.