For a deeper comment, I feel that the movie was grandly successful in a number of areas, and yet I can't help but feel that something was amiss.
Thoughout the movie it seemed as though I was always trying to follow too many thematic threads to see where they went. In the serial nature of a comic book, a writer/artist can freely explore new themes every issue even if the series ends up as a single graphic novel. Single movies, even when incredibly long simply seem to be a poor medium for exploring so many seperate ideas.
I can only point to V for Vendetta, another movie adaptation of the same (writer? Artist? one of the two I don't recall) work. The movie made substantial changes to the plot and even altered my perception of many key characters. While I was initially outraged at the changes, when I viewed the movie simply as a movie and not an adaptation of a beloved book I realized that the changes were, in all likelyhood for the better. Rather than explore the diverse themes of the nature of the hero, the potential blunders of conservatism taken too far, the evils and ills of warfare, the docile acceptance of the people and so forth, they delivered a streamlined version where there was little thematic conflict in most areas. At the end of the day, in V for Vendetta one cannot help but root for the murderous V, yet by the end of the saga in the novel I was hopelessly torn. Where V's goals of revenge are essentially in pursuit of the noble cause of freeing Britain fom tyranny in the movie, in the novel he undertakes his mission of vengence simply to plunge the nation into chaos.
When I watched the movie The Watchmen, I had not ever (and still have not) read the graphic novel. Yet, at the final accounting it seemed that only Rorsasch remained a hero, though he is revealed as being essentially powerless. The rest trade in their notions fo heroism for pragmatism and Viedht himself is painted as being nothing more than a well intentioned, well spoken murderous thug. I can't help but think I'm supposed to respect his action and grudgingly regard him as the hero, but I just can't bring myself to like someone who has plotted long and hard to murder tens of millions. Yes, he did it in order to gain world peace, but I can't help but think there had to be a better way.
In short, having never read the novel I can only assume that this problem is the direct result of too close an adaptation, but this is a damned if you do damned if you don't scenario. Most of the rest of my qualms are momentary at best. The softcore porn sequence springs to mind. But, in spite of these gripes I think the movie succeeded in more ways than not. I'll pick up the graphic novel here in the next few days so I can attempt to better resolve my problems with the themes. It might be a flaw of the novel but I suspect that's not the case.