This might worth it at pdf prices for some people, but its easily missed by most.
It doesn't provide much content for a hardcover price, has many reprints (often with changes that make them less effective) to options already available online for free, and the new stuff that is here mostly doesn't impress. I expect a high proportion of dud or "so what" feats and magic items in a RPG line book, but they seem higher than usual here. There's almost nothing here that got me excited.
I am mildly in favor of casting these new options in a Golarion context. I just wish they were better options and more of them.
This book has lots of interesting, flavorful, and useful options for many classes. Very few useless options, and many that you'll want without feeling guilty or overpowered.
I've enjoyed the last two bestiaries quite a bit, after a small slump in Bestiary 3, and wasn't sure Paizo could keep it up. Not only did they, this is my favorite one. I admire that they took the chance on publishing so many high-CR monsters and love the execution. They are consistently excellent and very competent opponents for your PCs.
I also liked the reprints, which make some obscure/niche monsters more generally available and improved. A comparison between old and Bestiary 6 versions will show the reprints received plenty of individual attention to improve them and make them more polished before inclusion in this this book.
And while this book excels at the high-CR monsters, it also has a nice mix of variety, with several low-CR threats being cool and/or scary. Buy it!
Do you want a lot of rules and options to help run a campaign set in royal courts and other elite social environments? Buy Ultimate Intrigue!
But this book is ok, too. You'll find many archetypes and feats that are of the usual quality (forgettable but not offensively bad) and a few well polished diamonds.
My favorites:
1. A bardic masterpiece that replicates the Commune spell
2. The Protective Luck hex makes enemies roll twice and take the worst when attacking an ally
3. A paladin archetype that gives lots of swashbuckler abilities at reasonable cost
4. A strong level 4 occult ritual that can serve as a daily party buff
5. A monk archetype that lets you swap feats for SLAs or advanced feats (w/o preqs) fueled by a new (Cha based) pool of energy separate from your ki, it's also well supported by feats, a case can be made for treating this as a standard archetype you need to justify not taking
6. The Perceive Betrayal spell, which is great for bodyguard or intrigue situations
7. New skill options for existing social skills, much better than the UI "here's a feat to do something you were obviously capable of by default before we published this" approach
8. The Silksworn Occultist. Easily the best 6th level caster when it comes to actual spell casting and SLAs, 9th level casters would be jealous if they weren't, you know, 9th level casters. But for breath and effectiveness in using the abilities and spell levels it does have it's really, really good.
9. The Chastising Baton, a magical rod. Adds +1 DC to all compulsion spells, and sickens the target for 1 round if they make their save. Only 5,000 gp and a new must have for serious Mesmerists, Psychics, and Enchanters.
My biggest disappointment is the Pageantry Discipline for Psychics. It has promise, but makes a big, easily avoided mistake in the spell list that overlooks a well known OA errata, and the first discipline ability by possible intent is basically useless, but as actually written is too powerful. Better editing would have made this a good addition, but I don't see how it can be saved without a comprehensive FAQ that a Player's Companion won't get. Maybe PFS clarifications can at least fix the bonus spell list error.
Lots of great stuff and a little bit of really, really bad
I would strongly recommend you buy this book, but I can't give it more than three stars because it has some really poorly conceived and edited options in here that should be mildly embarrassing to Paizo.
The mesmerist, spiritualist, and occultist options are generally great, a couple of bad archetypes and unclear rules ("holding" panoply occultist implements) aside. As far as I can tell the medium and kineticist stuff is of similar quality, but I don't care about those as much. If you want more options for these classes absolutely buy this book and you won't regret it.
Where the book falls down is the Psychic items and spells section. I can agree that this was arguably more necessary to grow the class than an archetype or more disciplines would have been, but the implementation is pretty poor. Most of the magic items are uninspired psychic retreads of (bad) arcane options that in some cases already worked fine for psychic casters. The spells have some decent options, and a couple of weak options, but the real problem is that there are two absurdly strong options. One allows you to daze lock a creature even on a successful save (at 3rd level!), the other is basically a Moment of Prescience god mode that applies to almost every roll you do for 1 full minute. I think you can easily solo higher threat CR creatures in melee with this spell and a few standard buffs. It's that ugly.
Publishing either of these spells would have been irresponsible, publishing both makes me doubt Paizo takes this line seriously anymore with respect to maintaining the integrity and balance of their game. PFS will ban the hell out of them, but having this sort of awful munchkiness out there as an idea that someone at Paizo thought was ok to publish is troublesome.
My final complaint is that there are a few more than the usual (already disappointing) level of poor editing and rules mistakes that we've come to expect in the Player Companion line. You have an unprecedented casting time of "1 full round action" on some spells (a big problem on Psychic classes that need their move action to add metamagic or center and avoid concentration penalties and not an innovation that should be dropped in without explanation), missing explanations of partial saving throws, and a couple of other minor signs that this needed a better development pass from a responsible adult.
That aside, you should reward Paizo for the good things with your money and put the good options to use responsibly. I just hope the bad things get more attention in future products and don't become a trend.
Everything about this book is great. The high level background on the First World (time, magic, fey immortality, history) is comprehensive and surprisingly detailed given the limited space they had to work with. The section on the Eldest is fascinating and sets them apart from your ordinary demigods, plus the fey obedience boons are generally very strong, inventive, and thematic. The gazetteer of First World locations provides dozens of great ideas to develop your own adventure locations, and the Bestiary adds several interesting and creative new critters to serve as allies or adversaries.