I think I've posted about it before, but I felt like the concept of mimics from Prey (aliens shapeshifting to lay ambushes) and Perfect Vermin (a metaphor for cancer where you are smashing up monsters camoflauged as furniture) would have been very good.
The mimics in Prey are just another enemy, the first time I tried Prey I was very disappointed in them, and now I recognize them as just a bit of flavor and not the main point. And Perfect Vermin is a low effort indie game. But a person could make an incredible horror game out of playing this idea full hilt.
I think what you'd do is have very small and detailed maps. The monsters have a devastating attack, maybe just a straight-up one hit kill. The player can likewise just kill the monsters by hitting them. The key is the AI. The monsters should be able to try and anticipate player actions and ambush them accordingly. In general, if the monster is in the player's vision, they should stay completely still. If the monster knows it can safely ambush the player, it should. The interesting play comes from how much the player looks around. Stare at an object too much, approach too aggressively or cautiously, and the monster knows you'll try to kill it, so it either runs and hides or kamikazes you. Engage one monster and others will go for you while your back is turned. Pay too much attention to an object, look away, and it will relocate.
If the AI was clever enough, you'd have a very tense, paranoid game, because you're not only agonizing over every object in a cluttered room as you try to slowly and safely clear it, but you're also playing mind games with them, and them with you, too (trying to play coy to lull them into false security).