You play a telepath. Possibly a spy or a private detective. Your job is to infiltrate a facility where a warlord/terrorist/mob boss/etc. is holed up. Your only weapon is your brain; you possess telepathy on a level unmatched by anyone on the planet. Rather than just stealthily navigating the facility and knocking the guards out with weaponry, you navigate with your mind, feeling the TP field around you (three dimensionally), searching for the minds of the guards you must overcome. The navigation is done with a hot-cold color spectrum; the closer you are to red, the closer you are to locking in on someone's brain. Once you find a guard, you can attack it, either by attempting to find a fear impulse (by sending a series of glyphs/pictograms; the game would be without words or speech) or by just plain knocking them out. Your powers are limited in range; to knock them out, you'd need to be pretty close. The closer your are physically to a person, the brighter the color would be. So if you're searching for someone all the way across the building, you'd pick up a dull red when your mind got close to them as it roamed. If you stealthed your way closer to them without being detected, you might get to a bright red where you can then try to knock them out.
For challenges, on the later levels you could have tinfoil hat guys who you need to be line of sight to use your powers on (and then can only resort to the fear impulse; you'd basically have to play a lightning round of glyphs back and forth, looking for their greatest fear before they had time to shoot/call for help). And you could also have big, clanky robot sentries, devoid of any TP pattern. You'd just have to learn their patterns and move with stealth to avoid them (using your sense of hearing rather than the sixth sense; playing it by ear, I guess).
Like I said, it formed somewhat out of a dream. Also out of a desire to redesign the typical stealth/FPS game to remove the reliance on physical weapons (SEE ALSO: Portal). Lastly, I was trying to envision what telepathic perception would be absent any other data (I was pondering making the character blind and/or deaf). How would a game look where the character moved not only in physical space, but in mental? Thinking about the farsight gun in Perfect Dark, and about how it would feel, how it should feel to a gamer unbound by walls.
If I called this game "The Weapon", would Rush sue me, or invite me backstage?