Jonathan Case’s review published on Letterboxd:
"Violence begets violence." I Saw the Devil is perhaps the most violent film I have ever seen and it does a wonderful job of proving a point to not only its lead character but to those who watch it. This is a merciless 2 hours plus long film and it feels longer given what it inflicts on the audience. I didn't understand why this was classified as a "horror/thriller" before watching it, but I know now.
This is a twisted tale of revenge going to the extreme in order to prove a point about the normally cathartic genre that is the revenge film. Revenge films often take the action route and show the hero off as someone righting a wrong in a way that is not normally acceptable, but because it is a movie and they are so horribly wronged, we root for the hero to succeed at achieving their goal. What I Saw the Devil does is show you what that does to a person. Life is not wrapped up neatly in a bow once the end of the road is reached. There are consequences, and not just physical consequences but emotional and psychological consequences. A metamorphosis occurs and they are forever changed. It's a tragedy. It's a reality check.
The "cliché" and "unfulfilling" ending where the hero doesn't go through with their actions is usually looked down upon and considered weak even though we know that is what is right. The reason? Because it is a movie. The difference here though, is that for once, I watched a hero become such a monster that I didn't want him to succeed. Sure the villain is still far worse, but the protagonist is no longer a protagonist and so, he no longer is deserving of any kind of retribution. That final shot of the mental breakdown is the most poignant and the cherry on top of this bloody sundae of a film.
I have admittedly never seen any of Kim Jee-woon's other films, however, it doesn't take an expert to see just how talented a director he is. His staging is perfect and the action, always captured from the perfect angle for what is happening. He captures both quiet tension and fast paced fights equally well. The cab scene and the hallway shotgun assault sequence both stand out above the rest in terms of action. There are also some very inventive scene transitions too. His direction made this watchable. In the wrong hands, this would be nothing more than a wholly gratuitous mess (and there is still a lot of gratuity). He also had phenomenal actors though too.
Choi Min-sik delivers another outstanding performance. He delivers the most evil character I've ever seen in a film. His character is remorseless and so perfectly presented that it made me worry for the actor. Then there is Lee Byung-hun. I wondered how this would go, him being opposite Min-sik and all, but he more than impressed me. He goes from grieving victim to merciless monster at a pace that feels too real.
To sum up, I Saw the Devil is an experience that left me numb. I can't say I enjoyed it, but I understood what it was trying to get across and because it did it so well, it is difficult for me to knock it even though I find it to be thoroughly excessive. It is a critique of itself in a way and in that way too does it succeed. I don't know if or when I will watch this again but at least I'll know what I'll be in for: a very harrowing experience.