I Saw the Devil ½

Charlie Kaufman: The only idea more overused than serial killers is multiple personality. On top of that, you explore the notion that cop and criminal are really two aspects of the same person. See every cop movie ever made for other examples of this.

Donald Kaufman: Mom called it "psychologically taut".

Replace "the notion that cop and criminal are really two aspects of the same person" with "revenge begets more revenge and violence" and "every cop movie" with "every revenge movie," and you've got all you pretty much need to know here.