First of all, I loved this movie. Then I heard that The Watchmen
was the ultimate graphic novel / superhero story, so I read that and loved it. So, I was interested in reading this to continue my exposure to the graphic novel genre, but also out of my love for the story and want to deepen my understanding of it.
My husband got this for Christmas (from one of our cats) and he didn't mind if I read it before him since he has so many other books backed up to read. I read this quickly, making it the last book I read in 2008.
Overall, I liked the movie better. Part of the reason is that the movie exposed me to the plot first; the surprise and initial enjoyment wasn't there when I read the book because I'd already experienced it through the movie. I also believe that I would have been more confused if I hadn't seen the movie first because like other posters have commented, all the men look very similar and I would have had a hard time keeping them straight without some background.
A fair amount of the plot was changed to make the movie, but overall for me the ideas remained the same, so it didn't bother me too much. However, I didn't like the ending of the book as much. It just dropped off.