I had already read the graphic novel and...

Rating: 8/10 (20 March 2009)

... this movie was an improvement!
The best adaptation of Alan Moore's works I have seen to date. Not truncated, not shy and - if you enjoyed Batman sledging bad guys then THIS IS IT FIVE TIMES OVER. A whole gang of superheroes sledging bad-guys, and occasionally, kicking the **** out of each other!
Alan Moore might be - as far as the IMDb is concerned - the most accomplished author in the genre of graphic novels. "From Hell", "V for Vendetta", "League of Extraordinary Gentlemen", even (arguably) "Killing Joke" have all resulted in big movie adaptations. And this one stayed honest in every way to (at least my reading of) The Watchmen.
All the one-liners, the key incidents, political comment and Alan Moore's sense of irony was all conveyed fluently in this adaptation. It corresponded with (my reading of) the graphic novel - frame by frame, line by line - and where it did seem to deviate from the graphic novel's exact story line, it actually improved it!
Furthermore, I was pleased to read *67rocks* review, considering he admits he hadn't read the graphic novel. That says a great deal for the movie's success in delivering the message that the story meant to convey.
PS: Will "Lost Girls" be adapted into a movie? 8P Somehow, I doubt it...