One thing that added to the atmosphere of horror games, that gave them some measure of unpredictability and made them just plain scarier, is parolling enemies. Remember Return to the Cathedral? The Cradle? In the former you see the enemies patrolling the lower floor of the Cathedral. You are on a balcony on the upper floor, hiding, pondering which way to go, then the doorlock screeches behind you and a hammer haunt walks in, screaming as it notices you... *shudder*