There are really a lot of things that impressed me about Papers, Please especially from the perspective of game design: it clearly is a rather unique game in terms of structure and progression, and because of that I think that it had to build its own learning curve, inserting additional mechanics and elements of complexity time after time in a way that came out to be extremely anxiety-inducing as much as actually genuine and interesting.
Papers, Please is also and above all a story of choices, priorities, freedom, and bureaucracy, and it is a story that manages to unfold itself crystal clear in front of the player by confronting him or her with increasingly complex situations: how willing are you to put your job position at risk to do what is right? Is it right to take bribes and put others' lives at risk if there is a shortage of money at home and a sick child? Are you willing to put your family's survival in front of your own life?
I really loved everything about this game, I think it represents a way of understanding the simulative potential of video gaming in a very original and not at all trivial way, showing how even behind a tedious and repetitive mundane job passes a universe of situations and complexities, incredible people, hopes and frustrations.