It was THE first graphic novel, and one of my favourites.
I'm man enough to admit that I still subscribe to Heavy Metal, and Watchmen is still one of my favourites.
There's a lot of people that are having varying things to say, but the one thing I've picked up from people who've seen the screener early is that it would do a LOT of good for you to have read the book first.
I hear it doesn't do well as a stand-alone movie.
That being said, it's kind of long, is VERY violent (comic book violence attains a whole new level of impact when brought to the big screen), drags in the middle a bit, has its schlocky parts, and the ending is different than the novel, but overall is an enjoyable film.
Personally, I'm looking forward to seeing it, as are quite a few of my friends. As long as you go into it realizing it's not going to win any Oscars, I don't think you can go wrong.
I also enjoy reading the movie reviews at Rotten Tomatoes.
http://www.rottentomatoes.com/m/watchmen/
$0.02 (CDN)