Like most graphic novels, I think much of Watchmen's success is in its refusal to conform to the typical comic-book genre. Neither the graphic novel nor the movie is for the faint-hearted. It explicitly exhibits various and sundry atrocities without any bearing to spare their audience from seeing them. This one is not for the kiddies, that's for sure.
Regarding graphic novels in general, I have always been a fan of Neil Gaiman. It was he who introduced me to the graphic novel with his Sandman series. To this day, Preludes and Nocturnes and Seasons of Mist remain my favorites. In all honesty, I hadn't read Watchmen before seeing the movie, though I got the jist of the storyline from reliable sources before viewing the movie.
As is the case with most graphic novels, the story isn't just about protagonist super-heroes using their abilities to thwart the evil plans of the antagonist super-villains. It goes deeper. Watchmen asks the question, "How far can a hero go down a path of darkness, if that path will ultimately lead to humanity's salvation." This concept has been explored on and off by comic writers for years, the most popular of which is Batman, who inherited the name "The Dark Knight" when he chose to inherit a vigilante persona and become a scapegoat for the police, while secretly helping them and protecting the city. I love this. When any book chooses to address ethical questions, real or hypthetical, it stimulates the intellect.
In the movie, there are a group of superheroes called The Watchmen, who gave up being heroes. One of these, the supposed antagonist of the story, unleashed a plot that killed millions, but in so doing thwarted nuclear war, which would have made the human race practically extinct. Consequently, he made one of their own a common enemy of the global state. Like Batman, the hero he implicated became the scapegoat, and consequently united the entire world in fighting a common enemy.
The hero he implicated is called Dr. Manhattan, an enigma of sorts. He was the only one of them with truly super powers, and really the only one who could defend himself against humanity. Since acquiring his powers, he troubled about losing his humanity, and became very stoic. In the movie (and in the book), he is usually nude, though his powers make him appear blue and luminescent. Disconcertingly enough, he remains male and is depicted, again in both the movie and book, as anatomically correct. It is somewhat humorous at first, but one wearies of it quickly.
The most common hero throughout the movie was one called Rorschach. Dressed like an English gentleman taking a walking tour through the countryside, he is anything but. An older man with murderous tendencies, a vigilante justice code, and the ability to use some really cool gymnastics, he wears some sort of fabric over his face with a constantly undulating pattern. This fabric, he calls his "face" (another Batman alusion, in my opinion, since Bruce Wayne sometimes referred to himself as his mask). He is the coolest hero in the story, hands down. Imagine Wolverine wearing an trenchcoat and a fedora, walking around New York or some such city.
The movie was excellent. And the level of adherence to the graphic novel was truly amazing. Most of the scenes look as if they were peeled right of the panels off the comic. Most of the lines in the movie were verbatim with the book. It was uncanny in this regard. Where were these guys when Narnia hit the big screen?!
The movie takes place in an alternate reality, in the eighties, and with multiple allusions to this era. Modernized eighties music pervades the movie, along with music from earlier decades. In some cases, it is a profound trip down memory lane. I found it interesting that backdrops of the New York skyline had the World Trade Center.
If you can stand the bloody violence, exaggerated nudity, pervasive language, and explicit sex scenes, this movie is a must-see for graphic novel fans. A very real thrill ride into the world of superheroes.