There are hard to watch movies that make repeated viewings seem like a gruesome chore and there are hard to watch movies that pay off repeat viewings. This one falls squarely in the latter camp and is one of my favorite Korean horror flicks ever.
On a wintry night, a young woman is stuck on the side of the road. A man pulls over to offer her help but things quickly turn deadly for her. Unfortunately for the killer, the woman's fiance was a secret agent with the government (like a Secret Service bodyguard type). The grieving man sets out to find the killer and make his life a living hell. Very bad things happen when these two forces collide and I don't want to give away any more.
Sometimes, the "hero" is so brutal, you feel sorry for the serial killer. But then the killer will go and do something horrible and you are back in the corner of the grieving badass. As one pursues the other, the movie becomes a sort of Eyes Wide Shut of evil as the killer encounters some of his fellow enthusiasts and some amateurs along the way. The balance between hunter and prey is always tipping and the collateral damage is truly frightening.
This is not an easy movie to watch (one scene, where a man's genitals get hammered, is rather brutal) and features all manner of violence, cannibalism, torture and depravity. However, if you want to challenge yourself to see how far you would go for revenge, or just want to see a satisfyingly dark movie...check it out.