Far more than a mere 'monster book' this sets the scene for many creatures from a collection of 'ordinary' wild animals (and domesticated ones, too) to exotic and spectactular ones that may serve as full-blown NPCs or interesting adversaries (or both).
Lavish illustrations and loads of background, from that which a naturalist might study to the lore and tales told about each one, accompany the necessary game mechanics to run each one to good effect. In many cases, the text provides ideas for when your characters may encounter the beast in question, sometimes even a full adventure involving it starts coming to mind!
Creatures are grouped by type, where appropriate, which makes it easy to flip through to select just the one that you need. A 'corporeal undead' monster for example - skeletons, ghouls and more. Notes on religions revolving around the undead are in the text, adding extra depth to what otherwise might be a mere monster list. More demons than you can shake a candle at, and plenty of novel creatures not to be found in other games.
Ogres and orcs, dragons and drakes... even dangerous plants (!), there is a fine succession, a veritable parade for you to flesh out your world with. Slimes and oozes, spirits, swamp fiends and swarms - on they come!
An excellent monster book!