Look to other games that have come before that excelled at delivering scares. The Resident Evils, the Silent Hills, and so on. Bioshock, Dead Space, etc.
Even some games used scare tactics intermittently. Ravenholm from Half Life 2 or the swamp that preceded the Flood int he first Halo game spring to mind.
Also draw on movies. I recommend The Mist from 2007. It uses the titular effect to conceal the many creatures, and in that way it causes the viewer to exaggerate how menacing the creatures might be. The movie happens to be based on the Stephen King book which also inspired Half Life.
When you can't see monsters it causes your mind to fill in the blanks. I still find it unnerving to hear creatures running all over surrounding me in a FPS, and when I cannot see them, argh! I venture cautiously...
I would recommend implying carnage too, with a destroyed environment, bodies strewn about, and blood splatters. It causes the player to wonder 'what happened here?' and put them on the defensive.
And the most common trick used? Make it dark and shadowy. Your environment is a bit too well-lit.
Last edited by ddelisle : 08-09-2009 at 02:56 PM.