Green Zone is a movie about a soldier, leader of the team hunting for WMDs in Iraq, tries to step over the official army bullshit line and the red tape and actually achieve something. He gets a lucky break in finding a lead on general Al Rawi (the Jack of clubs in the famous Iraqi card deck) and stumbles upon a secret that explain not only why there are no WMDs, but also why (or better said how) the Americans came to enter the war.
As a movie it is a neat action film. A slightly less physical Bourne in Iraq, but with a political edge. It features shootings, helicopters, drama, conspiracies, evil suits, mislead Americans (represented, of course, by a journalist) lots of people speaking Arabic for no good reason other than they are Iraqi and lots of cramped alleyways.
There was a controversy about how the movie seems to reflect upon a real story. The real-life Roy Miller (actually Richard Gonzales, but shh, Miller sounds better), who also worked as a consultant for the movie, has issued a statement in which he clearly states the plot is a fantasy. I like how he ends the statement: "The real story of the hunt for WMD is, in fact, more interesting. Maybe one day, someone will want to tell that story.". A bit sad and a bit hopeful. Maybe History Channel will pick up on it in a few decades, when the heat is off ;)
Bottom line: well done action thriller, better than most, but then I like Matt Damon as an actor, so maybe I am biased. Certainly above average.