I would'nt rate this movie a rather good one or a bad one. This novel by Alan Moore is way too dark, too complex and basically too smart. Maybe we're aren't old enough to understand what is life or the true nature of mankind and sort shit like that. Well, basically thats about the plot-the human nature thingy.
Rorschach- is my choice of character in that movie! xD
If you were to ask me whether should you watch this watchmen, I would say not too. Its running time is about 165 minutes. Yup, but not to say its that Unwatcheable, its still can-watch that kind of feel then slowly you'll feel dumb. :D

Anyway, I should get the novel. I heard it was brilliant!