I just came back from seeing this. I enjoyed it.
I read the work when it was first compiled as a graphic novel, and maybe once since then but at least a dozen years ago. And I've not read much of Moore otherwise, nor much of comics since then, so I'm not sentimentally attached to the material, author or anything else.
It was a fun afternoon movie. Pretty well-done for a fantasy comic-book film. Some excellent effects. I really liked Archimedes and Mars.