The Book of Beasts: Monsters of the River Kingdom had me on board at page 3, when the first monster entry is found. The Addanc is a Beaver/Crocodile hybrid that builds dams to create small lakes to hunt from. Not only is this a Brilliant idea, but being a hybrid creature, and having a black and white entry, it gave me a nostalgic longing toward the feel that the First and Second Edition monster manuals had. The rest of the book keeps on pace with this, offering several original ideas (like monstrous vermin versions of the water striders that skate along the top of still waters) as well as a new twist on some old tropes, such as river raider versions of a pirate skeleton crew.
The book is 36 pages, with black and white art, and an easy to read font. Most of the entries occupy a single page, or a double page spread side by side, making printing single entries a painless process, a rare thing for a down-loadable PDF. The Monsters in the book are all CR appropriate, and several fill unique roles. There are undead, monstrous beasts, a dragon, a plant, a construct, and even an ooze, spreading the love evenly to several creature types.
As a bonus, the last few pages are occupied by two new new gambling games, a new drug, several new diseases, simple templates and haunts, offering a rare thing for a monster book: something besides monsters. My only complaint in the entire book is that these rules are presented in an appendix format rather than having a few paragraphs to explain the nature of the rules and that they expand upon rules originally presented in the Game Mastery Guide. Still, their inclusion at all more than makes up for their presentation; you would be hard pressed to find many monster books with more than just monsters in them.
Most monster books have a few monsters you look at and think “i can never use this” or “what is the point in this creature?”, but not this book. Page after page it offers rules you can use, all united by a common theme, while still offering very different options on every page. This is an all around fantastic book which i recommend highly.
[5 of 5 Stars!]