Underused ideas

So, I'm curious, what's your guys' favorite underused idea? Something only barely touched on in film, book, or game. For me, it's zero gravity combat, as that's pretty much always FPS games that have it, but they don't take advantage of it. For a proper way of using it to its fullest, utilize the fact there is, factually, no up or down. Have the shoulder buttons adjust your up and down. What I mean is, when you look "up"-your up- pressing the "ascend" button will have you go "back" relative to how you were facing a moment before, as an example. If done properly, I feel it could lead to some interesting levels in science fiction games.
Let me know what yours is in the comments.