I've been looking forward to this book for months, as our current campaign has a changeling character in it, and we were hoping for more material to work with. Now that it's here I'm blown away by it; I think I can safely say this is my favorite book in the Player Companion line.
This book has great options and information for changelings, hags, and witches in Pathfinder, all in about equal measure. The contributions here go beyond the rule additions however; the book really expands on what we know about hag ecology, the lives of changelings, and the role a patron plays in a witch's spellcasting career. In the case of the patrons, I finally feel like a witch's patron is as active a participant in her character as a cleric's god, which is saying something!
Our game group is going to get a lot out of this book now and in the future. I'd recommend it as a steller expansion on both character options and in-game lore.
Full disclosure, I purchase all Pathfinder books relating to the gods or religions as a matter of habit, and I'm a bit predisposed to like them.
When this book was first announced on the blog, the description led me to the impression this book would have actual quotes and excerpts from the holy books of the Inner Sea region, perhaps on interstitial pages. This is decidedly not the case, and while I was initially crestfallen this book really turned things around on my first read-through.
GMs interested in building a realistic world through inclusion of unique treasures will find a lot to love in the early sections of the book, which detail noteworthy theological texts outside the standard holy books (some of which are quite rare, or circulate in different editions with different uses). Plenty of related magic items are found there that would also make good crafting quests or unique gifts from servitor's of one's god.
Overall the flavor of the book, and the detail it adds to the setting, is tantalizing; so many new offshoots of major religions are introduced, as well as new points of contention among major sects. These 32 pages have made me want to play followers of deities I previously found uninteresting, thanks primarily to the apocryphal subdomains that help clerics specialize in a certain tradition of worship that might set them apart from the crowd.
Which leads me to my favorite thing about this book... NEW PALADIN CODES FOR EMPYREAL LORDS! I was over the moon about this, Chronicle of the Righteous is a top-5 book for me and this really compliments it in a great way. Dwarven gods and gods of the Dragon Empires also feature here in smaller share. In less than 5 pages the Paizo staff has here considerably opened up options for paladins, including some long-overdue codes (e.g., Ragathiel's). Additional details on who might become a paldin for these deities and how will help give players good backstory ideas.
The two best additions to the game in this book are the sheer number and variety of traits (many of which could be used quite creatively by players), and the new archetypes related to the obedience feats. Ever since Paizo introduced boons and obediences I've always been on the lookout for new ways to use them other than prestiging, and this book delivers on that. If you're looking to snag some boons without prestiging, you need this book!
Now, for the downsides. Pharasma does not feature in this book, so those looking to find new options for her worshippers will be dissapointed. However, given the number of empyreal lords and lesser deities featured, I think it's to be expected one of the main pantheon wasn't going to make the cut, and Pharasma has plenty of mechanical support already. Secondly, meditative spells (while interesting) are somewhat limited in their utility, and probably won't become a universal feature in people's games in the short term. I like these spells, don't get me wrong, but I wouldn't buy the book just for them.
Overall, not what I expected, but still a real treat! This book is crammed full of great tools and inspiration, and makes a great addition to the Pathfinder line.