Steve Youngblood said:Everyone (I've even caught myself doing it) says this, which is just the wrong way to look at it. If a movie can't stand on its own without familiarity with the source material, then it's just not a good film, which may be the case.
All in all, I think the problem is just that by attempting to stay so true to the book, it set up a film that is quite unlike what people would come to expect. At times, it WANTS to be a blockbuster, action-filled film, but those scenes are few and far between and not at all what the book was about. Thus, reading the book isn't a requisite for enjoying the film, but it incidentally prepares you to know what to expect. Also, it gives you an attachment to the characters that is very important for the success of most comic book films. Not only do you not know any of these characters if you haven't read the book, but you also have no frame of reference for what they're supposed to be. Try explaining to people the characters were loosely based on Charlton Comics characters. You'll be met with a blank stare, as the characters Moore crafted are more memorable than the characters he used as a template, and the Watchmen was a completely self-contained story.
All my friends watched it without no prior knowledge of the book, besides the basics. They got everything, all the twists, flashbacks, the works. I even quizzed them afterwards. They loved it.