Just finished reading the book. As InTheShadows said, this series is incredibly faithful although the reporter has been removed from interactions whenever possible. The higher-ups come off better because the book explains their decisions in better detail. They even have a methodology: "maneuver warfare," pushing ahead without establishing a supply line or rear security. This was the first test of a strategy encouraged by Rumsfeld, and as an invasion it was successful.
Also, the book more clearly states that these guys were often the northernmost part of the invasion force, "the tip of the spear." That means the invasion of Iraq was at times fronted by a Justin Timberlake and Wheatus obsessed ex-nerd high on Ripped Fuel, who left the Marines to work the desk at a 24 hour gym, a guy who sang Gordon Lightfoot's Sundown while killing people, a dog-killing enthusiast who is now training to be a LAPD cop, and a Rolling Stone reporter.
And although they claim their disagreements with the text are damning and I don't think they are, in addition to Casey Kasem's rebuttal above there's also Major Shoup's, which is more reasoned and readable:
http://commentaryongenerationkill.blogspot.com/
In its comments section there is a lengthy rebuttal to the rebuttal by Evan Wright.