Andrew Corsini’s review published on Letterboxd:
This is not a film about serial killers.
It is not a film, sadly, about the Zodiac's victims. Nor is it about the Zodiac.
This is a film about obsession.
The men obsessed with hunting down the Zodiac, whether to catch him or just, as this film's protagonist, Robert Graysmith (Jake Gyllenhal) says,
"just so I can stand beside him, look him in the eye and see that it's him". Some of the greatest films in cinematic history have concerned obsession, from the obsession with Rosebud in Citizen Kane to Jimmy Stewart's obsession with Kim Novak in Vertigo to the obsession with the bicycle in Bicycle Thieves, perhaps because they inspire similar strong emotions in the viewer. In the case of David Fincher's film, this is about a very dark obsession, catching the Zodiac, and perhaps not for the reason of justice but solely just so they find personal relief. The gruesome Zodiac killer repeatedly cites the film, The Most Dangerous Game, about a man hunting other people, to justify his quest for bloodlust. At the opposite end of the spectrum, Jake Gyllenhal's cartoonist, Robert Downey Jr's crime writer and Mark Ruffalo's cop are all playing another most dangerous game -- hunting the Zodiac.
In truth, only the film's last thirty minutes is about obsession. The first two hours (it is overlong) is about the Zodiac's reign of terror.
In a bizarre twist, I found these first two hours boring and tasteless. Fincher uses very Hollywood trick in the book to dramatize the deaths, from the very 70s horror movie way these scenes are played out to the euphoric rock music that plays over the soundtrack while real people are shot and killed. You feel like the filmmaker is showing-off and, yes, it just becomes boring. The last thirty minutes, though, when the Zodiac's murder spree has stopped and where the obsession takes hold... some of the greatest scenes in twenty-first-century cinema take place in this last act. From a nervous date where Gyllenhal can't stop talking about the Zodiac and realizes Downey Jr's character may be killed, to an interview Ruffalo's character has with the suspect who may be the Zodiac. It's all so fascinating and dark and disturbing and I couldn't stop watching. John Carroll Lynch, who normally plays such nice guys, really transforms here and plays the suspect with chilling callousness. It's in these scenes where Fincher actually makes good choices with camerawork and editing.
The film's greatest scene though, one of the best in modern cinema, is where Gyllenhal follows a cinema expert down into a basement and realizes he may be face-to-face with the real killer. It's superbly done. A penultimate scene where Jake Gyllenhal finally meets Lynch's suspect is also incredible in its chilling simplicity. It's as if both men know they're meeting their nemesis.
You can criticize Fincher for turning the deaths of real people into a "boys' own mystery story". You might criticize him and the film , and Graysmith, for pinning the Zodiac on John Carroll Lynch's Arthur Leigh Allen, since disproven by DNA evidence, though I can't really feel sorry for a pervert and who knows, maybe he really did do it. The first two hours of this film are dull, tasteless and an insult to the real people, couples, mothers, working people, who were murdered by a monstrous serial killer. That last half hour, though... a masterwork.