Given the genre, I give this quite a high rating. The neo-noir mystery film genre is quite niche and as the slow burn of this movie displays - a story which is wrought with subtle, mild and indirect displays of specific cultural norms between Koreans.
Thus, I do think it requires more in depth knowledge of social customs, cultural norms between Koreans and Chinese (The protagonist and his "Suspect"). The story builds and builds, filled with beautiful cinematography and a great OST.
It is a genius movie if looked through that lens which I believe the story could be lost on many viewers because of that. This is like Oldboy, which only became a cult classic a few years later. I suspect, this film will be an inspiration for future directors and viewers alike.
Very underrated.