I admit I'm a bit of a fanboy for comics (big surprise?). I loved the Watchmen movie. It looks on the big screen crisper but frame by frame as it did in the book. The changes that they've made to the costumes etc seem very driven by the original artist.
The writer, Moore, doesn't have his name on the project because he is opposed to comics being turned into movies. However, despite his objections, this is a good medium for this story.
In true Watchmen style this is a very graphic movie that does not have a happy ending. Lots of sex and violence, but it is integral to the story development. As one of the earliest anti-hero comics it was always intended to be darker and grittier than the other things around it.

Some of the movie looks panel by panel and word for word. I'm re-reading the TPB now. Wow.

Some of the movie has the essence of the comic with updated graphic pop and bang. The artist for the original comic worked with developing the movie. It looks like they finally did what he couldn't do by hand years ago. Very visually beautiful.
Some of the movie, at its mildest, is no worse than other violent comic movies (Dark Knight, Punisher, etc.)
http://www.mtv.com/videos/movies/343653/exclusive-watchmen-clip-prison-break.jhtmlHowever, this is the movie at its mildest. Immediately after this these two heroes return to their fancy aircraft to have some super sex. The character that they are trying to break out of prison, an arrested hero, is killing prisoners bizarrely. The movie did not pull the punches it is as graphic as the graphic novel in violence and sex. A friend of mine summed the movie up in, "Dr. Blue Guy could put on some pants at some point." I think he missed some of the symbolism in the slow motion sex scenes and constant nudity of the characters. I wouldn't take my kids to see this one, but I'd go watch it again myself.
Just my 2 cents.