A Korea Times article mentions other aspects of the film:
"Yes, it is,'' Na said bluntly when asked if the movie was a social criticism. "Fury prompted me to write the story,'' he told reporters following the film's press preview in Seoul.One scene juxtaposes police sleeping in their car with a scene of horror, to which the audience I saw it with reacted audibly. The Joongang Ilbo article mentions it a bit about the shooting:
The shoot was tiring because filming went two months over schedule ― bad weather caused huge delays ― and the scenes were physically demanding. "Most scenes were shot in the dark and in heavy rain,” Kim said.The final scene took 40 hours to shoot. No wonder they looked tired. Also, Mark at Korea Pop Wars wondered whether the scenes of chases through hillside alleyways were actually shot in decidedly non-hilly Mangwon-dong, which is where the film is set. Here, perhaps, is the answer:
The chase sequences mainly take place in Mangwon-dong, but Kim’s role demanded that he spend a good portion of the film sprinting through Oksu-dong, Pyeongchang-dong and Bugahyeon-dong.At any rate, it's nice to see such a low-budget film doing well. If you're not put off by some realistic bloody scenes, it's well worth your time.