Mark Jewiss’s review published on Letterboxd:
I Saw The Devil tells a revenge tale that pushes the boundaries in a good way. Kim Ji-Woon's film will make you question where the acceptable limit is for taking revenge on a serial killer that has taken away the person that you love most in the world.
The two leads put in brilliant performances, but the stand out is Choi Min-sik as the sadistic killer. He plays this with such cold detachment and matter of factness that you can't help but be chilled.
There are moments of pure beauty throughout the film in the cinematography, most notably for me the snow fall throughout the opening scenes, contrasting with what we're being shown.
This may be a tough watch for some, but it's worth it. Think of it as a Korean version of Seven that takes place after the (Seven spoiler alert!) head-in-a-box scene, but Brad's character doesn't just shoot Kevin Spacey, he drags his revenge out over several days.
Slightly concerned that I liked this so much.