I have been a lifelong student of composition, and this book opened up a whole new realm of musical thought for me. There are brilliant observations regarding chromatic tonality, atonality, and structure that (although they are presented largely in the context of an analysis of Bartok's music) shed light on the development and future of modern music in general.
The book serves also as a fitting tribute to Bartok, a genius who all too often is written off as merely the modern adaptor of Hungarian folk-song. In this book the author demonstrates how the folk-song interest, and other fundamental Bartok building blocks, have a deep basis in the fundaments of life and the world.
If you've known Bartok's music speaks to you in ways you can't explain or understand, or if you just want to wrap your head around one of the most important contributions to the development of music in the modern era, then this book is for you.
I hope this review is more helpful than the one below, which seems to be more of a jumble of random thoughts, most of which appear to be associated with some other, more biographical work.