GMs can really benefit from this book; plenty of variety ranging from planar to material. A new animal companion (Cooshee) and aquatic 0-HD race (Locathah), along with the cool spells in the appendix, makes this a tiebreaker for would-be buyers wondering about player options. The creature write-ups are solid with decent-to-excellent illustrations throughout (black and white).
Without covering every entry, my favorites were...
...the ten-page Chaosiic article filled with random-anatomy tables and five basic variants to tinker with, plus two Chaosiic Lords, and a new plane, Corrupting Chaos.
...the Devil Doll; at CR1 this creepy "toy" can be used anywhere.
...the Junk Elemental; nothing says surprise like an animate refuse pile. Also, be sure to check out the Plane of Junk.
...the Lejnth. I like the devil-but-not-a-devil status.
...the Mâlite, Denizens of Mâl. I absolutely love this article, but there's only one example of the creature (or rather, its host). Also includes Mâl's planar stats.
There's many more I really liked (for no sane reason at all), but I'll stop here and recommend this for anyone that simply needs more monsters.