I'm a big fan of David Fincher; have been since Alien3. I never understood the slamming that film got. For me it was always better than Cameron's effort. I look forward to each new Fincher movie, and it was disappointing that I didn't manage to catch this one on the big screen.
Zodiac is a film about obsession -- one man's obsession over an unclosed serial-killer case. The man in question is not a cop; nor is he a journalist per se. Rather, he is a newspaper cartoonist, and the film follows his story over a 30-odd year period. The serial killer is Zodiac, the inspiration behind the Scorpio character in the first Dirty Harry film.
There are several great things about this film: the story; the performances (Gyllenhaal, Downey, Ruffalo, et al); the direction; the look; the feel; the scope; the ambition... But it's the latter that is the film's only problem.
The nature of the story is that little spurts of activity come in the case once in a blue moon, so what we end up with is an awful lot of "three years later"-type subtitles. This leads to a sense of bittiness, which is unfortunate. That said, I'm not sure how else such a story could have been tackled while remaining faithful to the source material.
I liked the film very much; it is a slow-burning thriller based upon character rather than action. After a second viewing, I score Zodiac 80 out of 100 (revised from an original 78).