FYI, I am not into this genre but manage to get a spot on my current top 5 list on K-Drama.

Story:
Episode 1-15 will keep you engaged as good cliff-hanger at the end of episodes.
It is a Dexter Love Story, where a psychopath may have a chance to get a love story, with crafty twists from writer to keep you clicking next episodes on Netflix.
Episode 16 is a near perfect wrap-up as every character get a proper ending, however 1 full episode for a closure is too long, therefore you can expect some unnecessary scenes and dialog. And it is 9.5 point due to usage of amnesia, my-most-hated-k-drama-element. In my opinion, this element is unnecessary.

Character:
ML: Good character development, and like union got some layer which is uncovered layer by layer with fun twist and mystery here.
FL: Consistent character through the end, fantastic mother, lover, wife and a detective (priority in this order).
Supporting Male Lead, Reporter: a joker who put a comedy-salt in a horror-bowl.
Supporting Female Lead, The Sister: Typical character in K-drama, melancholy, undecisive, weak, hated.
Villains characters are also good. It is not a single villains from start to finish. Most of crime K-Drama will have one Lex Luthor, but in this drama got Joker, Penguin, Bane.
Overall they are development for each character which is a must for me, and they are complex enough to get explanation why they become who they are.

Acting: Above average, I can't spot any bad acting in this series. The Main lead suprisingly is good (had a doubt with his acting on previous drama I dropped - Scarlet Heart something i guess).


Music: Honestly i don't pay attention to any music. So it will follow story's score.

Re-watch: I don't like to waste time on re-watch. So it will follow story's score.