try using cosmetic fogs on the map to create shading, and hiding zombies in the shaded areas, another thing you could try, is dropping all sound effects to 70%, especially if there was background music. Then when you wanted something to be scary, you play it at 100% volume, an idue to people turning up their speakers (they usually do) it'd sound like it's 130% volume, and much more surprizing.
The fog shading is good for small rooms, but fairly difficult for long hallways. However, it is something that I will try. As for the music, I've already got most of the ambient music set to 80 and horror music set to 100. It feels like I'm cheating if I do it too much though, and it might do more to annoy a person rather than to scare them. I'll keep experimenting with it though.
;p Wellm you need to like make mosters appear out of nowhere in the most "Unexpected" places, & enough, I am having trouble just massacring Zombies, d**n them!
Monsters so far will be coming from around corners, from behind furniture, from behind doors (just as you'r about to open it), from under the soil, from the occational fireplace, rising from the floor (even though you thought it was just another victim), bursting through walls, and even one or two will drop down supposedly from the ceiling (such as how the Bandersnatch does in the demo).
The key to making the game ten times easier is making sure you have enough distance between you and the monster before you even attempted to kill it. If it's too close, put the gun down and run like hell!