You should read this book for the facts in it, not for the author's very judgemental interpretations & simplistic assumptions because they are clearly biased by the view he wants to prove. Right from the onset Epstein insinuates guilt and crime. His stance is not neutral, and he repeatedly tries to shove his view down your throat. This irritated me a lot.
Throughout the book this attitude is very annoying, particularly his lack of thoroughness in his critical statements. For example, he limits himself to citing only two alternatives where three or more are possible. It often seems he only mentions the scenarios that would fit the bill of what he wants to "prove".
And to make matters worse, sometimes he goes on daisy-chaining such limited assumptions.
Other than that, the storytelling/narrative is suspenseful and the revealed facts are interesting. A passionate read, definitely not just about Snowden, but also the NSA, Russia, spy stories, history, China. Read this book to learn facts you won't find anywhere else, but make sure you separate the facts from the author's conclusions. I'm not saying he's wrong (nor that he is right), just that given the facts it is not possible to conclude certain things. The additional facts however help you open your perspective on the possible existence of alternative truths, and thereby be more critical on this whole, very important episode in history.