The haunting score by Jo Yeong-wook (particularly "The Last Waltz") is crucial. A compressed LK21 audio track (usually 128kbps) flattens the dynamic range. You won't feel the bass of the hammer or the whisper of the villain. You need 5.1 surround sound or at least high-quality headphones.
: A legendary single-take fight sequence that redefined action cinematography. The Vengeance Trilogy oldboy lk21 best