There's a temptation to over-praise I Saw the Devil on the grounds of sheer novelty: it takes a basket of ripe clichés and mixes them into something that you simply do not ever see in American cinema, however much each ingredient is individually over-worked to the point of moral indecency. 1) Serial killer 2) who has a particular hatred for women 3) kills a cop's fiance 4) sending the cop on a revenge bender 5) that results in the cop becoming almost as much a monster as the man he's hunting. Somehow, in practice this turns into something fresh and new even as you can call every story beat from miles away, and that overwhelming sense of freshness where there surely oughtn't be any gives I Saw the Devil just exactly the kickstart it needs to overcome the fact that it ultimately adds up to a whole lot of nothing, and it takes every bit of a half-hour too long to get there.

This is not unfamiliar territory for director Kim Jee-woon: his last film, and arguably his biggest splash in English-speaking markets, was the Western-cum-war film The Good, the Bad and the Weird, which did a fine job of deconstructing and reconstituting Hollywood tropes in a stunningly original way. I Saw the Devil is not ultimately as good as that film, which might be partially because the tropes Kim is playing with this time come not from the noble Western but from the disreputable slasher flick; on the other hand, it's all the more impressive that he and writer Park Hoon-jung are able to drag something unexpected from such a wholly formulaic subgenre, curving left when you expect them to veer right, pulling out a n "oh, but wait" every time you think you have the story dead to rights.

For example: the opening scene finds a young woman, Ju-yeon (Oh San-ha), stalled on a snowy road late at night. This is bad news. Worse news is the lumbering man, Kyung-chul (Choi Min-sik), who pulls up in a big yellow van marked with the unquestionably ironic legend "School Safety Van". Ju-yeon happens to have her fiancé, Dae-hoon (Lee Byung-hun) on the phone, and there's an unendurably tense moment when we watch him talking to here, wondering when the hell she's going to get snatched - it doesn't happen, not until after he hangs up, and she turns on the headlights to find Kyung-chul standing just feet from her car (an indescribably effective jump scare. He clubs her, and drags her off. The lingering feeling we get that we've been watching a torture porno is confirmed in the second scene, in which Ju-yeon is chained helplessly, with Kyung-chul idly wondering how he can cause the most pain to her, and then the scene ends just as he starts.

Quintessential gore movie stuff, which is why it's a bit unsettling when I Saw the Devil abruptly becomes a procedural about Dae-hoon, a secret service agent, using the considerable means at his disposal to track down Kyung-chul. It might not show from the way I've described, but every single aspect of the first two scenes - the pacing, the music, the lighting - screams that we're watching a slasher/torture film, and everything about the third scene onward says instead that no, we're definitely not. Instead, we're going to follow Dae-hoon as he laboriously tracks down the four men the cops think might have murdered Ju-yeon, coming at last to Kyung-chul for a climactic showdown- wait, no, he disposes of the first two in a matter of minutes and comes to Kyung-chul third, and the movie's barely a fifth over.

I won't belabor the point, but basically what goes on is that the movie tries on the conventions of a given subgenre for a few scenes, and then simply changes its mind and moves to the next, and it does this for all of its 141 minutes. Theoretically, this could result in a film with massive tonal instability and a personality disorder - that's basically what happened with The Good, the Bad and the Weird, although it was unquestionably deliberate in that case - but the effect is the exact opposite. Despite the fact that every individual moment of I Saw the Devil is trite to the point of exhaustion, and despite the film's willingness to own up to that fact - there are no less than three points where a character openly states the message that Dae-hoon is turning into a savage himself due to his quest for revenge - the effect as a whole is so excitingly loose that the movie does something no slasher, torture porno, bad cop picture or revenge movie should be at all able to do in 2011: it keeps us guessing.

Which wouldn't matter much, except it's a good film along the way: Kim's ability to stage a truly horrifying scene of violence shames a generation of American horror directors, and even most of the "extreme" films trickling into the West from east Asia over the last decade: the film is nauseating and horrifying and honestly upsetting - late in the game, Kim manages the impossible trick of playing cannibalism for laughs and still making it seem like the most ungodly of crimes - and never blithely exploitative of gunk and gore. Lee Mogae's cinematography includes from the expected noir shadows of the scarier scenes, but the most visually impressive parts are perhaps the normal, everyday parts, slightly hard and slightly sharp and just bright enough that they make you squint a little; a movie of raw edges that isn't right even when it seems like everything is working out. As cat and mouse, Lee and Choi make a great pair, trading off strength and vulnerability from scene to scene, Lee playing implacable, joyless perfection here and Choi being bloated and haughty there. The best part of the film, in fact, is probably the interplay between the two men, a shifting mixture of various moods, all of them ugly and brutal - it is an ugly and brutal world.

In fact, as a thoughtful exploitation film and a cutting depiction of the effect that committing violence has on men's psyches, I'd love to call I Saw the Devil a pretty great movie. Except it's not quite that; for all that it talks about the effect of violence, and for all that Lee plays it that way, the film is ultimately much more of a slick thriller than it is a psychological study, to its ultimate detriment. Plus, there's no ignoring the length: there is absolutely nothing about this story that requires almost two-and-a-half-hours to tell, and the fact that I Saw the Devil stretches out so languidly, though it allows for some passages of dread-inducing idleness, means that it is never able to build up enough momentum to completely succeed even as a slick thriller. Fix the somewhat contrived and hyperactive grand guignol ending, and there's a great movie that can be carved out of all this; sadly, good movies with a great movie hovering just under the surface are the most annoying good movies of all.