I'm pretty much just going to parrot the other posts here. I thought the beginning was a little slow, though I really liked the opening montage and I thought the song choice there was perfect (unlike in other portions of the movie). I was perfectly fine with the ending and I thought it worked better than the graphic novel version would have in a movie (works in the comic though).
The entire film felt slow compared to a lot of other films - but I have to say I enjoyed that. It was paced differently from an action film, something that fits the theme and tone of the film (note: I deliberately avoided reading the comic before the film).
It struck me as a "style-over-substance" film, but not in a bad way. It has lots of strong, impressive pictures and fitting music - sometimes it felt more like an "artsy" film than a big comic adaption, but then, I like a strong sense of cohesive style in films.
However, the characters were... slightly flat. While the film left an impression of gravitas, the characters did not. Rorschach was great and the portrayal of Dr. Manhattan also stood out - somewhat, because he did felt *alien* on occasion. The rest... was not uninteresting, but not particularly gripping either.
Furthermore, the film felt like it came too late. I think the themes of the film would have made more impact a when the nuclear threat was more pervasive - or even before the release of Dark Knight, which did the "realistic superhero" theme already- and better, character-wise.
Nevertheless, the positive aspects outweigh the negative ones by far, hence I think it's a solid 8. It probably could have been better, but not a lot, given the length constraints - because it does feel a bit rushed towards the end, suggesting that it had to cut a lot from the comic.
Cheers, LT.