I saw it in theaters and twice now on DVD and I still can't distill my feelings. I did read the graphic novel first, so I have a tough time judging it as a movie independent of the source material, but her it goes:
I actually liked the movie's changed ending - I think it was an appropriate change and worked better than the original. In the interests of not spoiling it for anyone, I won't discuss that further.
I found the soundtrack annoying. Using such iconic songs just didn't fit and was often tacky - playing "hallelujah" for the sex scene? Give me a break. An orchestral score would have been much more appropriate.
On the one hand, I appreciate the respect that was paid to the source material. Much of the movie was a frame for frame depiction of the graphic novel, and much of the dialogue was lifted right from the pages of that novel. But that was also the biggest problem - pacing that works for a comic book, doesn't in a movie. Dialogue that looks good in a speech bubble sounds wooden and awkard when spoken by an actor. It was also a 12 part comic book series. Movies are typically done in 3 acts (sometimes 5). The break points were obvious and awkward and just didn't fit in the flow of a movie.
So I guess if anything, I wish that they had taken more liberties with the script to properly adapt it to a different medium.