I thought these two recent R2 releases were excellent, both directed by Park Hoon-jung and starring Choi Min-sik (Old Boy, Lady Vengeance, Lucy):
- New World (2013)
https://www.eurekavideo.co.uk/montage/new-world
- The Tiger (2015)
www.eurekavideo.co.uk/montage/tiger-old-hunters-tale
Both contain graphic violence. The Tiger has some truly awful on-screen animal deaths, but all animals are of the furry digital/animatronic variety and their deaths weren’t gratuitous IMO. Like many modern movies, some of the digital effects were a bit overdone (fast moving animals didn’t look totally real) but the high-quality story/acting/direction/soundtrack made up for that.
A few have mentioned Oldboy (2003), which I also rate highly, but note this is part 2 of the Park Chan-wook The Vengeance trilogy, so also check out Sympathy for Mr Vengeance (2002) and Sympathy for Lady Vengeance (2005).
With the exception of Train to Busan, every South Korean film I’ve seen in the last decade or so has been at minimum very good. (Sorry to the other posters, but I found Busan repetitious, the endless screaming tedious and couldn’t wait for it to end. I did enjoy some of it though, like the train towing the zombies).
I also thought Man from Nowhere (2010) excellent.
One way I discover a lot of movies (and music) that I’d otherwise overlook is browsing Amazon’s “Customers who bought this also bought” list, e.g. load The Tiger b-r and check out some of the five star titles listed. Easy to fill a basket in no time.