It's been reviewed to death, already, so I'll keep this brief: much like Sin City, the film adaptation of Watchmen exhibits a respect for the source material and the fans thereof that borders on reverence. Many scenes are storyboarded straight out of the book, and much of the dialog is verbatim, including, fortunately, many of the best moments from the book ("I'm not locked in here with you, you're locked in with me!")
The book is incredibly dense, making a complete translation to screen an impossibility (even with the entire comic-within-a-comic subplot axed, the film clocks in at just under three hours.) Still, Snyder is to be applauded for getting as much in as he could. And for many well-crafted (if easy to miss) references--mostly visual--to the parts he had to leave out. The opening titles in particular tell a ton of the back stories that were woven into the original.
Casting was superb (though no amount of old lady makeup can make Carla Gugino not hot...I would have cast her as the younger Silk Spectre, and someone actually old as her mother.) Jackie Earle Haley's Rorschach in particular was stellar.
As much as I enjoyed it, I have no idea how it will stand up to a naive viewing. Actually, if you never read the book and have seen the movie, I'd be interested to know what you thought.
Anyway, all of the above is really just an excuse to post this, about the horror that could have been: