David Fincher's Zodiac is an odd sort of mystery, a story with no ending and a dogged, one-note hero. Whether or not you think Fincher is the next Kubrick, Zodiac succeeds because of the director's attention to visual detail and his wise decision to let a large cast of actors do their thing.
Zodiac is about something that I think more movies could feature, people who enjoy their jobs. Robert Downey's Paul Avery, a crime reporter eventually undone by excess, is the prime example. Avery is on the Zodiac story from the very beginning, and never loses his desire to outwit the killer. He's even willing to trade ideas with cartoonist Robert Graysmith (Jake Gyllenhaal), who eventually goes on to write the books that formed the basis for James Vanderbilt's screenplay.
How does one describe the perfect marriage of actor and role? Downey's roles have never lived up to his hype, in my opinion, but the dissolute persona he brings to every role seems like a gift from God here. I'll also say a word for the fundamental decency that Anthony Edwards brings to the role of second banana cop William Armstrong. One of the creepiest scenes in the film is the Armstrong-led investigation of suspect Arthur Leigh Allen (brilliant John Carroll Lynch), a scene which Edwards beautifully underplays. As some shreds of evidence begin to turn towards Allen, we're with the cops weariness of the case and need to put away the killer. Armstrong is the model of decorum with Allen, but his eyes give him away.
Zodiac is a feast for character actor junkies. Lynch, Pell James (victim), uncredited Ione Skye (near-victim), Brian Cox (Melvin Belli), John Terry (publisher), and Chloe Sevigny as Graysmith's wife. Although I thought the last act of Zodiac dithered a little, as Graysmith digs into the case to write his book. But Zodiac is a marvelously humanistic mystery, celebrating haunted lives and best efforts.