Oldboy. I love this movie. One of my favorite scenes was the "Hammer Fight" scene. It was just a wild ride.
BUT, a couple of friends of mine refuse to see it, because "it's too weird". Their loss.
Rumor has it, that Tom Cruise is interested in an American remake, much like he did with "Vanilla Sky", which was a remake of "Abre Los Ojos" (which was another movie people didn't like originally).