JM’s review published on Letterboxd:
I Saw the Devil is a strong narrative-driven revenge thriller. From the opening scene of the devil appearing on a snowy night to the devil appearing surround by calm plants, it's really the battle of the baddest. Having Lee Byung Hun and Choi Min Sik in one film is enough of a treat and add that it's a Kim Jee-woon film (who to me, seems like a version of Takeshi Miike, only more hits than miss).
As I said, this film has a strong narrative, it's a revenge film that does try to push the boundaries of disgust and horror. It's not horror because it's scaring, it's horror because the amount of blood and flesh is horrifying, enough to churn the insides of your stomach. As a revenge film, it succeeds. And I applaud it for being daring and bold and raw.
But as for characters, they seem to lack a backbone. We have two characters that are both trying to be the most horrible devil there can be...without much substance. We know why Byung-Hun wants revenge. We know Min Sik is a psychopath. But it just...feels empty. To me, I didn't feel the intensity of their feelings on why they want to do things so badly. And it can mostly be because we don't have any background on these two characters that are pitted against each other. It just feels souless.