What a great flick. I have never read the graphic novel, and had very little background info regarding the plot, history, etc,- I read the opening paragraph about the Watchmen on wikipedia, and the few posts here...that's it- but like several others here, I was hooked from the beginning and never lost interest.
Side note- Rox, I personally was seduced by the opening credits with Bob Dylan and the comic-like cinematography that gave so much depth with so little motion. I enjoy music that pulls me in two directions at once.
The characters were complex and complicated. I actually wouldn't have minded if the film went into even greater detail about their pasts and inner struggles, but I guess that's what the g novel is for, which I will try to make time to read.
I thoroughly enjoyed all the characters, but felt The Comedian to be the most intriguing. Ozymandias(sp?), IIRC, was left a little dry; I would have liked a greater background and character development for him.
Lastly, to end this rant, the fact that superheroes were shown to have "super issues", and no immunization to human drama, was truly a breath of fresh air.
Liked it, loved it, will likely see it again.