One of the more interesting revenge movies in recent (maybe all) revenge movie history. Definitely a big step above Death Sentence at least.
Min-sik Choi (of Oldboy fame) is a RIDICULOUSLY good actor. He just sells every scene he's in. Whether he's getting his ass kicked or killing someone, or even just driving around. He's just spellbinding. The other lead is good too, though he doesn't have as much to work with, as he plays most of his scenes as very stonefaced, but it works remarkably well.
It's an interesting film beyond most of this type in how it shows how a 'monster' is created and why they take on such practices. It's also a nice twist on the genre where it's the killer being stalked, and it's pretty violent if not somewhat unrealistic in how people repeatedly get their heads smashed in but somehow live. All in all a pretty interesting movie.