It would be a two-player, online co-op game, based on one of my favourite shows growing up, Knightmare (I doubt anyone on this board has heard of it, but look it up on Youtube, it was great).
The idea works like this- player one has a full view of the current area, but no control of the character.
Player 2 controls the character, but can't see anything. The two players can communicate via voice chat, so P1 has to tell P2 what to do.
It made for an excellent TV show (the reason the one exploring couldn't see anything is that they were really standing in an empty room, being superimposed onto the dungeon environments via early green-screen, so they wore a helmet that obscured their vision while their teammates guided them around the non-existent hazards), but would it be fun on PC/console?
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"I'm Commander Shepard, and you're standing in the biggest library in Citadel Space. Look me up."