One might say there is a pun in my summary line ... maybe even two. That aside, the movie is really tight when it comes on the story. It is quite fast paced all things considering and especially if you think about how much it does pack in.
Concubine may suggest some erotic encounters - and if that is what you think and expect you will not be dissapointed entirely. Just do not expect this to be focused on that. The scenes of sexual nature have a meaning to the story and to the characters. They also move along the story or plot lines.
Having said that, I guess this was discovered in the West because of the main actress being a part of Parasite. This goes to show you, there is much to find in Korean cinema that we haven't yet had a chance to view yet.
You may not like how characters act and what they decide to do. The questions if we couldn't just love each other instead of being so suspicious towards each other ... well you wouldn't have this tension filled movie otherwise now would you?