Great concept! But I didn't understand why I should clean up during the battle and maybe it might be better, when the soldiers wouldn't shoot at the janitor. Otherwise there's a conflict between cleaning up (and getting yourself in danger) and just surviving. Many times soldiers would stand around a lot of blood and corpses and I didn't see a reason to risk my (virtual) life to clean that part up. I also think you should show some kind of highscore or progress, to motivate the player to actually clean up (maybe the janitor gets paid by the work they have done and they need a minimum payment). Because of all the lasers, rockets and so on flying around the player would still need to dodge those, but having the soldiers aiming at the player might be to stressful.
Oh, and I love how corpses are bleeding, when you are carrying them around. That is a great effect.