The most greatest part of perception of the scene is wall textures. No, they don't have to be HD, they just have to be realistic, I guess. I have a few projects and in 1 of them there are no textures at all, only colors at walls. And know what? Even minecraft with it's 16x16 could have horror scenes, but not a game without wall textures.
Yes, you have textures at walls, but they are almost without any... anything, you know.
I'd made a few maps for CS:GO - and some times it's creepy even in editor, even when I'm just using standart CS:GO's textures. Let me show you:
http://files.gamebanana.com/img/ss/maps/568931633db8b.jpg
http://files.gamebanana.com/img/ss/maps/568933a92188c.jpg