Edgar Cochran’s review published on Letterboxd:
Be not overcome of evil, but overcome evil with good.
Kim Jee-woon has created one of the best and most morally, physically and psychologically complete cinematic experiences about the repercussions of revenge in human beings after Lino Brocka's Philippines masterpiece Insiang (1976) as we witness a supporter of justice slowly being demonized out of emotional impulses and a self-executed sense of justice up to the degree of becoming a monster in order to fight the monster.
Expertly shot, the tranquility and symmetrical balance of the landscapes is ambivalent to the brutality of the film which serves as a constituent of a larger and more relevant hypothesis about dehumanization. My opening passage kept repeating itself inside my head while I was witnessing a crime film which extreme relentlessness has pushed many to consider this as a horror film, a statement which boils down to subjective interpretation (it is not my case). Halfway through the film you think the show is over, but you realize there is still more than an hour of running time ahead of you. This remaining time makes a strongly intelligent and necessary exercise for the reflection of modernity: the justice system is flawed, since it is based mostly on the theory of utilitarianism and the biased philosophy of "I can do whatever I want as long as it doesn't hurt anyone else". Revenge is another biased doctrine that repays an X amount of harm to the exerter of injustices as long as X≥1. This "1", however, is relative, and in its unmeasurability, it knows no ethical bounds. Hence, the aforementioned exercise the film makes consists in making the viewer ask itself the boundaries that self-executed revenge should reach until reaching to the conclusion that revenge is not the answer.
Cards are turned upside down. This is one of the few films that makes the bold move of putting the protagonist in utter disgrace without a sense of victory, because there is no victory in personal justice unless we allow God to take matters in His hands and execute His justice. Ours is biased, destructive and self-destructive. Sure, films and other artforms are escapism mechanisms, and a film might root for revenge stylistically without necessarily agreeing with it morally, like a Tarantino flick with 88 samurais and a blonde or a movie theater full of Nazis blowing up. The idea of revenge predates ancient literature. The consequences, however, have not changed.
Refusing to belong to the police procedural crime subgenre like Memories of Murder (2003), Zodiac (2007) and The Secret in Their Eyes (2009), I Saw the Devil's title makes a reference of looking at yourself in the mirror when you want to take the matters in your own hands in order to get things subjectively "even". The protagonist representative of justice suffers a transformation and, unwillingly, ends up morally belonging to the other side while innocent victims pay the bill during the process for the irresponsible actions of kids wanting to get even. "Punch me in the face and I'll punch you back." The film is endlessly more brutal emotionally than graphically, and that is why it excels.
Dissonant to my previous analysis, might I add that I found this to be an excellent dark comedy? Beyond everything that has been said, I found this consistently funny.