Although I avidly read comics, I have never gotten into Alan Moore. I have read a couple things by him (League of Extraordinary Gentlemen, The Killing Joke), but I have never managed to get through his iconic stuff: Watchmen, V for Vendetta, etc. So bear that in mind.
I found this movie interesting, but too long for what it was. There were some beautiful, eye catching sequences (particularly the opening credits), but these were also very drawn out. I wasn't that interested in the characters, so I wasn't willing to wade through so much flashback and slow unraveling of the mystery. Really, the opening credits were the best part of the movie, which raised expectations, only to fail to meet them.