Okay, I've been out of the game scene for a while so stop me if this has been done. I have an idea about a game played within the mind of a person in a mental institution. It would be a sandbox-style game with free form game play. Each level a different locale or with a different feel to it.
The first is the asylum itself, the second could be an 'infested' version of the asylum to represent how the patient views the asylum itself. Think slime and odd growths, unnatural colors. The deeper you progress the stranger things get. Each of these sandbox levels would open up a new ability that the 'mental patient' can use once you complete the level.
After the first sandbox level is completed the linear gameplay begins with the mental patient trying to escape the asylum (that is coincidentally) conducting illegal experiements on the inmates. The rest of the game would include sandbox levels for more powers and linear levels that progress the gameplay.
Telekinesis (Object Manipulation)
Pyrokinesis (Fire Manipulation)
Clairvoyance/Clairaudience (Remote Viewing/Hearing)
Psychic Blast (Obviously a damaging attack, cone-shaped)
Mental Chains (Disabling attack)
Telekinetic Shell (Damage Absorbtion)
Telekinetic Flight (Obviously movement-based)
More to Come