The book starts with an account of the Abu Ghraib prisioner abuse scandal and then goes back to 9/11 and begins again from there. It's mainly about how the Bush Administration has botched the war in Afgahnstan, and the way we went to war in Iraq and the mistakes that have been made there. It also includes information about mistakes the CIA made in the lead up to 9/11 and the Iraq war. He ends with an overview of how our actions have impacted the Middle East as a whole.
The main thing that has changed since the book was published in 2004 is that our intelligence about Iran indicates that they are not as close to building a nuclear bomb as we had previously thought.