I've read many, many books on Scientology and I think I can safely say that this is the most well-written of them all. The beautiful prose made this an absolute joy to read (even if I read most of it sat in a hospital car park!), and it tells a fascinating story indeed.
I love the history of religions and this book is the definitive history of Dianetics and Scientology. For people who have only the vaguest of interest in the church, this book will give you an easy to read but in depth look at the history of the church. Even for people like me, who've read their fair share of Scientology history, there is still enough new information and a fresh perspective on oft-repeated events to keep it interesting.
And the history is intertwined with the story of Paul Haggis, from his early life through his time as a loyal public member to his apostasy. It helps imbue the narrative with a human story told by a master of his craft. It doesn't get much better than this.
There are excellent tellings of the stories of Quentin Hubbard (L. Ron Hubbard's son who committed suicide) and of David Miscavage's early years. And some little insights into John Travolta's journey inside the church.
Buy it. Read it. Love it.