Firstly, it's mostly because a survivor left the area
Secondly, the game is terrible! How would you think it's "pretty good"?
I think its a cool concept of out of control, since human beings are very spontaneous and unpredictable. I think the animations are nice as well and the mechanics work well for reloading and killing things.
Huh, never knew people would give positive feedback... And well, thanks for rating, really appreciate it :).