One of my favorite Korean directors is Kim Ji-Woon. I have liked every movie he has made. One of them, "A Tale Of Two Sisters" has been remade as "The Uninvited" in the US. And my copy of "The Foul King" came with a rubber wrestling mask. His latest film, "The Good, The Bad, The Weird" played at the International Film Festival last year, and may get a release this year (fingers crossed). But my favorite film of his is the gangster film "A Bittersweet Life". It is the story of a mob enforcer who feels sympathy with someone for the first time, unfortunately it was with the mistress of his boss. Things go wrong and there is lots of bloodshed. Here is the trailer for the movie.
If this looks good, then search on youtube for the whole movie as someone has posted it with subtitles. It has been 4 years since it came out in Korea so I doubt that it will get a US release, which is a shame.