Much of the foundation of this book will feel familiar to any existing fans of D&D's planar adventures (Planescape in particular) but pushed through the particular dark and dynamic lens of the Scarred Lands. The core cosmology is an abbreviated great wheel - Etheral, Astral, Shadow, Dreams, 4 elements and 8 aligned planes (each home to one of the gods of the pantheon). If it had just left off at that, this would have been an excellent resource for someone looking to jazz up Planescape, or to run a Planescape style game with a harsher tone, and it would have been worth 4 stars for that (and the supporting rules material). The extra star is earned by the Zodiac realms, one for each of the 16 constellations of Sharn and accessabel only when their sign is ascendant. Each of these realms is a bounded space, and while some are just extended lairs for Big Extraplanar Thingees, a handful of them are really quite interesting as idea seeds and potential adventure hooks.
I picked this up because I'm a planescape nut who enjoyed the Scarred Land material I'd read previous. I only accidentally discovered that this book existed, but it was definitely a good find.
[5 of 5 Stars!]