Idea

My Idea is for a horror game that detects your beta waves using a brainwave headset to attempt to gauge your fear/stress levels. When these are too high the game gets easier, the less scared you are the harder it becomes (the opposite from Nevermind).
This is an interesting way to implement a dynamic difficulty system.

Plus there is the possibility that a heart rate sensor could also be used along with the beta waves for even for accuracy.
Another feature that could be implement is mini-game level where you have to not blink for a set time and if you do, you are killed by a creature/ghost.

This could also be used whilst watching a horror movie to get brainwave and heart rate feedback for research.