Directors Cut?

From what I know the director's cut is the cut that was distributed in America. The South Korean version is the regular one. Unless you got your copy imported from SK you've probably watched the director's cut.

Director's cut is actually trimmed just as much as it is expanded, i.e. certain short scenes are taken out to streamline the film and make it faster paced. I know they also edited a tiny bit of the violence out - i.e. shortening the shots where Sun-woo is getting stabbed or shot because he was a bit too indestructible in the original version.

Director's cut is better though.

Here's a test - in the versions you've seen, when Sun-woo leaves the girl's apartment and picks up his cell phone, does he swerve around a car (which is actually the cheating boyfriend coming back after the coast is clear)? Because that's only in the director's cut.

http://www.movie-censorship.com/report.php?ID=3230 this also has details. Most of the scenes on that list were actually "removed" in the director's cut though, not added.