I was able to find this book in the library after it was discovered that Mark Felt was indeed Deep Throat. The book overall is a good, fast read, but don't expect to get any inside story about being Deep Throat (which he denies several times in the book). What the book is instead is a solid description of the FBI bureaucracy, especially in the 60s and early 70s.
More importantly from a historical perspective is that this book is also an unapologetic defense of his mentor J. Edgar Hoover. For example, he characterizes Hoover as being more pro-civil rights than just about anyone else in Washington, such as being against the Japanese internment camps in World War II, refusing to bug offices of a President's opponents etc. Hoover apparently was more pro-civil liberties than Felt himself, as Hoover tried to pull the plug on certain illegal activities which Felt allowed to continue. He refutes many of the dark allegations made against Hoover, such as the investigation of Martin Luther King, although I don't have the background to know if his description of these issues is accurate. Still, it is very interesting to get an alternative point of view on the subject.
Felt is very even-handed, as he complains almost as much about the Kennedy administration (especially the Attorney General RFK) as he does about Nixon. He complains that both Kennedy and Truman did not take the Red Menace seriously enough. The one organization to which he had unqualified loyalty was the FBI itself. Because of this, Felt resents the attempts by both the Kennedy and Nixon administrations to interfere with FBI investigations.
The book is not perfect. True to his career as an adminstrator, he sometimes spends too much time describing bureaucratic minutiae that do not have much relevance to the story. That being said, the book gives a fascinating description of the late Hoover era at the FBI, and shows at least some of the motivation, if not the exact details, of why Felt became Deep Throat.