It's digital age horror, Hitchcockian suspense, Korean police procedural, and a dash of Nolan non-linearity. I didn't know which way it was going, and I don't want to ruin it for anyone else. It starts off quickly, introducing the protagonist who has the bad hobby of covertly intruding on others lives by rifling through their possessions, in their homes he is retailing. And soon find himself in the clutches of an even worse obsession. There are some technical problems with the film. The flashbacks are not well limned. The Korean texts on cards and reports and smart phones are not closed-captioned so you lose a bit. And there is always the difficulty of keeping everybody straight with the unfamiliar names. So you must pay close attention, which will make the resolution less of a surprise then it might be. That said it is still easy to admire the scripting. The acting is very strong. I'm a great admirer of the radiant Lee El who plays the female detective and made the lugubrious My Liberation Diary watchable.
If you are the patient sort and can give it your full focus, you are in for a treat.