The Bestiary 4 for the Pathfinder Roleplaying Game has been one of the more favorites of the Bestiary series for me and I'd like to take a moment to tell you why.
To start, the Bestiary 4 has added everything from new types of fey to additional golems as well as the more prominent and popular Kaiju, Great Old Ones, and Empyreal Lords. Paizo's inclusion of these creatures that've gone on to become pop culture legends in their own right is a direct result of the designer's dedication to getting their monsters right. The Bestiary 4 is an awesome sourcebook and stands right up there with the Bestiary 3 in terms of 'fantasy verisimilitude,' hardening gamers resolve against such villainous foes as Cthulhu himself.
Not every book is a perfect image of idolatry however and the Bestiary 4 is no exception. While it's true that this book is littered with new baddies for your players to chase and new races for their characters to face, it is also bogged down with what seems to be an over-saturation of multiple page monsters. This isn't necessarily a bad thing, but it does seem as if several of these creatures could've used a proverbial trimming before being posted.
If you don't mind a bit of length though and you want more vile beasts for your players to square off against then the Bestiary 4 is yet another wonderful book to add to your collection and one that comes Five-Star recommended by your Severed Ronin.