Searching for something unsettling rather than terrifying for the Hallowe'en period, I happened upon Parasomnia by Acatalept. It's perhaps best described as a futuristic chrome version of the Theseus and the Minotaur legend.
Except you're not Theseus. Theseus hacked the game by bringing in a ball of string, killing the Minotaur and escaping. You're (currently) one of the preceding generations of Athenian youth sent in as sustenance for the monstrous Asterion and doomed to die.
The game is unfinished at the moment, serving more as an anxiety taster experience. The developer flavour text tells you, "In the hypnogogic twilight between sleep and waking, something haunts you / hunts you in this maze..."
You're deposited in the depths of an improbable maze; all chrome surfaces and occasional weird floating sculptures. Pulses of light briefly illuminate your surroundings hindering your navigation as much as they help you. The light pulses change, speeding up to match a beat which you realise is pursuing you through the maze and quickening as whatever it is gets closer to you.
It's a simple idea but one which contains a well-executed anxious and uncomfortable experience. I played a couple of times and in one I think I saw the monster itself which did spoil the effect, though.
As I said, it's not a finished game at the moment, more a proof of concept knocked together as part of October's Unreal Engine Game Jam. The list of features to-be-added involves some basic sound and performance improvements as well as some interesting maze generations ideas. One is a Cube-like setup where parts of the labyrinth would move around, a second is having procedurally generated labyrinths and another is never being able to turn back...