Was the required reading too much for you?
Yawn. Let's go straight to the low brow insults instead of attempting to discuss the movie in rational/serious fashion. Part of my beef with the movie lies in something i feel plagues korean cinema, and how poorly this movie matches up to the superior thrillers that nation has graced us with.
SPOILERS for this trash movie
The plot was dumb, like really, really, really dumb. Essentially all the movie is is this supposed super-cop hunting the killer down, beating him over the head with a stick(and this is damn near the only thing the guy does, just hits him in the head with shit repeatedly), and then letting him go, then repeating it. Somehow this was supposed to be some horrible torment, supposed to be satisfying revenge. It was pointless. And that really was the extent of his revenge, just wacking him on the head and letting him go, only to return and do it again. laughable.
Then we have what has become one of the biggest cliches in all of cinema, the Korean devotion to the saddest, most gut wrenching, kick in the nuts endings possible. Such "resolutions" certainly have their place and have certainly led to some powerful, amazing thrillers/dramas from that country, however the small handful of successes have led Korean filmmakers to pollute their output with such final acts, to the point where it's become a joke. The likes of Memories of Murder and Oldboy came out and now they all think that's the way to do it. In America we have the generic, boring, cash out "hollywood happy ending", well with korean crime dramas/thrillers you get the exact opposite and it ends up being even more forced and hamfisted. I Saw The Devil is one of, honestly perhaps the single, worst offender.
What makes it so bad here is how incredibly stupid the protagonist is rendered in order for the plot to play out how it does. This is without a doubt among the dumbest, most inept, ineffective character in movie history. That's especially bad cuz he's portrayed as this supercop sort of figure, yet we see him fail so miserably so often. It just didn't make sense seeing him make the mistakes he makes, to see him this pathetic. It all feels so incredibly forced, it IS all so incredibly forced.
The whole, "revenge is never satisfying, revenge only breeds more pain/turns you into a monster" thing has been done FARRRRRRRRRRR better. Fuck this movie, just watch Oldboy again instead.
It is well shot though, has some great performances, the car scene is brilliant, the suspense is top notch. But that plot, good god, just trash.