May I ask how do you fall through floors, I haven't fell through one floor yet. It is running WebGL so google chrome is best for it. As you referred to temporarily stuck in lifts, it usually only happens when you are touching the pipe and a solid is above, but apart from the bottom small lift, it shouldn't cause too much problems.
Good game but I think it is really hard to kill them, it takes at least 3 shots and with the pistol it's quite slow. What would bring more fun if you would like a machine gun and then increase the amount of zombies, just a suggestion. I think mouse is fine to control it xD