This is a foreign film (South Korea) so it loses points for it's voice-over work even though it's fairly well done. The plot follows a man who is imprisoned for 15 years for, initially, no apparent reason. Upon being released he seeks revenge while unraveling the circumstances behind his imprisonment and the identity of his captor. It all culminates into one of the most shocking, revolting, and incredible endings I've ever seen in a movie.
It's extremely violent at times and definitely isn't for everyone. But it has to be one of the best Asian films out there.
Alright, Asian cinema.
Oldboy is an excellent film, surely one of the best Asian films of this decade. If you liked that, you might like Brotherhood of War (Taegukgi) and Sympathy for Mr. Vengeance, both of which are Korean productions.
EDIT: Oh, and make sure you get English subtitles. Unfortunately, some subs, like the dubbed versions, aren't good translations of the originals, but there are some that suffice. I find the best English subs at my local Asian video store or if not, Barnes & Noble and Borders have a mighty big foreign aisle of decent subtitled versions.