This book has a lot of options, as most Player Companion books do. Reading through it, I liked most of the options from a flavor and mechanical standpoint. While nothing stood out as 'NEW OP MUST HAVE', I thought a lot of it was fairly good and not totally useless.
As an example, there is an advanced rogue talent that gives DR 2/Adamantium and can be taken multiple times. While not the best rogue talent of all time, it certainly has its uses, especially for enemy NPC rogues.
The majority of this book details a lot of the oceans and seas throughout Golarion, along with sunken treasures and the occasional NPC. It has a ton of flavor text and pretty good art.
It also goes into the nitty gritty details on movement and combat underwater, even changing a rule in the core rulebook about "cover from the water's surface".
If you plan on doing anything underwater, pick this book up. If not, you probably can do without it.
So much of this book is just reprinted from older books. There is some original stuff in there, but is it enough to justify the price?
Another issue, they nerfed some of the things they re-printed, specifically the Lore Warden Fighter Archetype. Terrible idea, as the disparity between martials and casters is already so wide, why make it worse? As the saying goes, martials cant have nice things.
This Bestiary has a lot of really cool monsters and solid art. Its a good book. Go buy it.
Two problems hold it back from 5 stars.
1) The creatures within are almost all CR 10 or higher. Most games don't make it far enough to fight super high CR monsters. Even if your game does get high level, it is sometimes more easy to apply templates to mid CR creatures.
2) It feels rushed in a few places. Several monsters that are ported in from adventure paths, such as the Erodaemon Daemon, have had their flavor text hacked down to the bone to squeeze things onto a single page.
This adventure path gets back to the basics, and has a healthy dose of wilderness encounters. Lots of hobgoblins to fight, but there are other critters too. I like the art for the hobgoblins and bugbear, very nice.
This book started it all for Fighters in 2106. Finally, the class gets options that lift it from bottom of the barrel.
Combine whats in this book with the combat stamina system from pathfinder unchained, get the armor master handbook and magic tactics toolbox, google "Iron Caster", and enjoy playing fighters that are amazing.
This book is not really 'bad', just middle of the road IMO.
It excels at flavor text, but falls flat on mechanics. A lot of the Traits / Items were already published in previous books, so there is very little NEW stuff to play with in this book from a mechanics standpoint, and what little new stuff there is, most of it is sub-optimal.
The one exception to this is the new horses, these open up more options for Cavaliers, which is always nice to see.