It's a well-worn concept, but it's true: some of the very best horror is scary because it evokes, rather than fully illustrates some kind of terrifying concept. Hints at a reality too terrible to imagine (which, of course, helps us imagine it). It's like a subtler "show, don't tell," more of a "sketch, don't paint."
That's what Dan Sanderson's Pacific does so well. It hints at a terrifying, ever-changing space. A bunker, maybe. There was an atomic apocalypse, perhaps. And you wander these halls, opening and closing doors, finding clues about what happened that will forever tantalize, and never tell too much.
It's a spooky game, in its atmosphere, but a scary game in what it implies: a sort of solipsistic hell, where there are consistent rules, but you can't really trust reality.