This film feels more like a pilot for a series. I'd even say it feels like an exposé for a series -- the movie's plot could have been the first half of the episodes, with the later half dedicated to the resolution of the main character's backstory.

The plot seems unfinished, some parts of it feel rushed, and it's unfortunate that a lot of backstory just gets told via the older detective's thoughts. I also would have liked to see more of all characters, and more of how they grow to like the main character. As it is, we still get a surprising amount of character development, especially from the team leader. (Heo Sung Tae is a highlight, as always.)

I think if the writer might have originally planned to have this produced as a longer series. There's a surprising amount of world building there, the characters all seem to have much more backstory than what we got to see. I certainly would like to watch this as a longer series, if it ever gets made.
Well, who knows what happened, at least they got a small budget for making this film, right?

One thing that is probably better because of the short duration of the movie: There was no time to force a romance subplot into it.

Overall, the movie does what it can with its short time and low budget, and it is a nice watch for a rainy afternoon or so.