It was hard to balance it with the time frame. I wanted it easy enough to pickup, but hard enough that once you know what you're doing its not "easy". I think my personal highest was 136.
Occasionally you get bad odds and to many skeletons will spawn to early. But the idea of the game is eventually you get overrun by them and die, or you make 1 mistake and die.
You need to be really proactive hunting skeletons until score 10-17 to get your first upgrade as quick as possible, which will improve you survivability loads.