i have two ideas, one is a story based idea and the other is an mechanic for a game:
-you play as guy with multiple-personalities; your the sane one, the other is insane, and the last is a psychotic killer
-(this is an idea for a horror based game) the main character wears glasses that he needs to see with. if he runs for too long his glasses slowly slip off his face and you need to occasionally adjust them or they fall of and you see everything extremely blurry. i think this would be nice because it adds an "ohhh shit" moment when you running from something and if you loose your glasses you have to frantically search for them while blurry objects move in the background
you blurry vision would be a creative way to play off the same idea that silent hill did back in the day with the fog and their bad graphics, it lets the players imagination create the monsters