its not the greatest, i prefer it over most of the superhero movies weve been forcefed the past bunch of years.
i love the ozymandias and dr manhattan characters, if you read the graphic novel its way better, between the chapters theres all these little cool back-stories revealed thru like newspaper reports and hidden files. specifically rorschach isnt nearly as gimmicky and far less annoying in the book, (theres also a moving graphic novel or whatever they call it, thats way better than the movie if you dont mind the format of a moving comic)
alan moore litterally wants nothing to do with any of the movie adaptations of his writings (including V for Vendetta) just takes the $, that dude is the man.
he also wrote the best batman/joker graphic novel, its called the killing joke. and as a bit of a spoiler it ends with an epic joke.
EDIT: if you know any batman enthusiasts that arent too young for a more clever/brutal version of the stories, get them this book for their birthday or something, its really good