Nothing to do with the zombies, that's for sure. They're generic enemies, and the general "scary" tactics game designers use suck. I'm normally a melee/long-range (aka shotty-sniper) character, so I do my best to keep them in the right range and knock 'em out one by one.
What scares me is when you're down on your last hitpoint with 3 bullets and you're so close to the exit door, but there's about 5 zombies blocking you from a clean run. That dread of knowing that in only a few seconds you could be forgeted five ways from Sunday and have to restart the entire level over again.
Gameplay is what scares me most, and so more designers should look into loving with their players
