I recently read Silent Warfare: Understanding the World of Intelligence, 3d Edition. It was a quick read -- I made it through in a couple evenings (and with two young kids that's an achievement) In general, I think it's a good primer on how modern intelligence works in the context of the government, but I'm of course saying this as someone who has no first-hand knowledge of the topic so I can only compare it to other books I've read.
To wit: it wasn't nearly as interesting as either of James Bamford's books -- The Puzzle Palace: Inside America's Most Secret Intelligence Organization or Body of Secrets: Anatomy of the Ultra-Secret National Security Agency. Bamford tells interesting stories. Silent Warfare takes a more "just the facts" approach.
It's more on par with Allen Dulles' The Craft of Intelligence: America's Legendary Spy Master on the Fundamentals of Intelligence Gathering for a Free World although The Craft of Intelligence had a little more meat to it than simply explaining how an intelligence agency works. But as an introduction to the intelligence community, Silent Warfare wasn't bad. It's probably unfair anyway to compare Silent Warfare to any of the other books mentioned here since it's more of an academic text than popular nonfiction. In the end, I think it was definitely worth reading, and I'm likely to refer back to it later.