What I found really a shame about this game (because of wasted potential) is that lack of leaderboards.

But then again, I find this a shame about most games, especially DRM-free ones.

The last game I remember to pull it off was Dustforce. DRM-free support AND somehow they managed to keep it clear of cheaters.

Still... even with leaderboards with lots of obvious cheaters, I still think it's nice to at least compete with myself and scores that seem reasonable. And it would be nice to have at least something like that in Zombie Night Terror.
Seems like almost a given to me as well: time it takes to complete the level (both real time and game time), zombies that got killed, maybe scores for ways of killing humans - sum it up some way - done.
I just feel that it could've added quite a bit of replayability to a game like this.