In fact, it's such a product of its time that I've heard people criticize it on that level. The original series by Alan Moore came out in the mid-eighties, and relies heavily on the fear of global destruction and mutual annihilation. The movie's set in the same period, and I've heard complaints that the movie lacks the same impact the comics did, because we're no longer in the same place in history. I suppose the alternative is to either modernize the entire plot (which would have ended very, very badly), or not do the movie at all.
There's actually a lot going on behind the "do we need a Watchmen movie?" argument. I think there's a bit of a nostalgia element at work--for a lot of people, the Watchmen is the first truly great comic series they ever read, so any adaptation pales by comparison. And this adaptation is so faithful that there's not really anything terribly new if you've already read the comics--as comic blogger Rachelle Gougen says, the reason for fans to see the movie is to watch the story come to life. And, of course, there is also the issue that Watchmen creator really, really doesn't like comic book movies. (Feel free to read to page 4, in which he states that the reason Americans like superheroes is "America has an inordinate fondness for the unfair fight." Gee, why didn't they use him for promoting the film?)
And one should always, always take into account what Alan Moore feels about a subject, because
the scariest comic book writer
ever to walk the earth.
Anyway, this movie is probably the best movie based on an Alan Moore comic ever to come out, and after V for Vendetta, that's actually a positive thing. It's got a lot of harsh language, graphic nudity, both male and female, and really, really graphic violence. If you don't mind any of this, then you're going to have a very enjoyable experience. Also, Rorschach's inner monologue is every bit as hilarious spoken aloud as I thought it would be. It's like Batman, if he accidently wandered from Gotham to Sin City.