A game like this on Oculus Rift is my wet dream. Not interested in it on any non-3D platform. On 3D the only gameplay mechanics you will need are naturally in the brain (adrenaline, cortisol, etc)--just create interactions that produce those and what else do you need? This is why I can't wait for 3D, the focus will be on creating immersion through interactive, creative environments that play on millions of years of brain evolution. Just think about it-- your brain will believe you are in a real environment, you will get that weird pit in your stomach when you descend rapidly onto a planet, your heart will race when you hear a growl behind you, or a giant leg crashes near you all of the sudden; a game like this would be insane.