After reading a few of the other reviews I feel I just have to put my two cents in.

Some say that there should have been more information given at the onset about the different characters and their situation.
Without giving anything away, I think that we were meant to be left to piece together who these people are and their situations in much the same way as the characters themselves are trying to understand who they are and where they stand in this world. It is unclear to some of them as much as it is to us.

And that's the genius of this piece.
Without explanation, we are pulled through this scenerio as we try to figure out its boundaries. In the process, we cannot help but feel confused, anxious and unable to brace ourselves for the emotional impact.

Its been a challenge to review this work without giving away what transpires.

The special effects are dramatic and impactful. I didn't notice the music, which for me, means it did not distract.

And the acting is excellent. I thought that each role was handled so believably well. That includes Bae Suzy, who took some hits from other reviewers.

All I can say is, let yourself take this journey. Explore where the film takes you. It may lead you to some interesting thoughts and emotions.