This book provides a thorough background of everything you need to know about the Realm. Giving the widespread influence of the Realm, this book is worth having even if your campaign is set elsewhere. In addition to covering Realm society, culture and geography, it describes the Immaculate Philosophy in detail.
I have only two complaints about the book. First, some city maps would have been nice, especially of the Imperial City. Second, there are no details on the Great Houses: you need to go to the Dragon-Blooded core book for that. On the other hand, if you buy this book, you are likely to get the Dragon-Blooded book as well.
[5 of 5 Stars!]