This drama was odd. It was essentially a fictionalized and more psychotic version of the Stanford Prison Experiment from the 1970s. The fact that the ringleader was in many ways a sociopath from the very beginning was definitely a recipe for disaster - and an interesting spin on the tale of what happens to ordinary people when they get unlimited wealth and power. I had a few small problems with the storyline - it was never entirely clear to me how 4th floor became a part of the elite since she was from a lower floor, and I think it would have been better if each episode had began with explaining how each person came to accepting this offer as was done for 3rd floor in the first episode. When there was finally more revealed in episode 8 it came a little late for understanding the motivations of characters in the previous ones. Still, interesting plot idea, and excellent acting from a very small cast.
What I did not like, however, is that there were a couple of episodes that were essentially nothing but torture p0rn - it wasn't a psychological thriller or mystery, it was just large quantities of extreme violence portrayed in a way that I felt was excessive and beyond serving the plot. Showing it continuously took the sadism far beyond using it for shock value, and in my opinion was detrimental to telling the story. That doesn't make it a bad show, it was simply not to my taste.