This movie has some pretty bleak things to say, metaphorically speaking, about love and relationships (of all kinds), and it's a workable suspense film, too. Part giallo, part procedural, part character study, it also has some surprisingly black-humored moments -- like the murder of one character by weight-machine, or the impossibly overstated catastrophe that follows the disposal of a victim in the middle of a highway (Hollywood 'thrillers' END with huge car crashes... this one has its big explosions in the middle, and ends with quiet horror).
Although there are plenty of nasty happenings in this movie, and a lot of bloody body parts popping up throughout, the really disturbing and frightening things are the implications of what's going on. It's pretty easy to guess who the killer is, though there are some good red herrings that distract the viewer's attention. However, it's absolutely impossible to guess the killer's motivation, and the REAL meaning of the whole film, until the last few moments.
I'm still unsettled from having watched this for the first time. I'm certainly going to go back and watch it again, probably several times -- because I'm going to have to live with this movie for a while before I can say I've come to terms with it. I especially want to be sure of my interpretation of the girl's last line to Detective Cho. Of course, I know it's supposed to be ambiguous, but I'm probably not going to be able to sleep until I'm sure in my own mind...