Five stars because there won't be another book like it. Even if someone somehow dredges up even more, deeper secrets, it will only be building on and because of Annie Jacobsen's work.
Sure, it helped a little that I was halfway through re-watching season 4 of the X-Files when e brought this one home. But most of the book is about aerial espionage and nuclear testing, so don't get your Lone Gunmen all excited. Of course, it's a lot of pretty incredible, well-written, dramatic first-hand accounts of work on aerial espionage and nuclear testing--things our country can be proud of achieving, things we're lucky we survived (I'd never heard of the USS Pueblo before), and things our government should be ashamed of. (As someone who works with a tiny amount of radioactive material every day, I did a lot of shuddering for those 50s, 60s, and oh, wait, 70s, 80s and 90s workers...)
That said, if just the phrase "Area 51" gets your X-Files/conspiracy theorist side on alert, stick with it until the end, where Jacobsen shares some awful, shocking information that I'm sure will resolve questions for some people and only fuel the debate for others.