This book is amazing for anyone looking go do some adventuring in the Astral Plane. It provides a wide variety of rule variants to help explain the weird enviroment that is the Silver Void, as well as in depth explainations on why things interact the way they do.
This book also covers what happens when gods die, is when of the best resources for Githyanki society, and details some cool monsters, as well as the many types of psychic wind.
The scan can be a little difficult to read, and is laden in Planescape cant if that isn't your style. Otherwise, really good read.