Man, I am a huge fan of Asian cinema!
Oldboy is pure class. Choi Min-Sik is one of the greatest actors on earth right now. Have you ever seen "Crying Fist" where he plays the amateur boxer? That film is awesome, seriously reccomend you checking it out.
The third installment of Chan-wook Park's revenge trilogy is really good too. It's called "Sympathy for Lady Vengeance". Very similar to Oldboy and some argue, even better... I find it hard to pick between the two. "Sympathy for Mr. Vengeance" was pretty good too, but not up at their level in my opinion.