A local multiplayer game, 2D side-view, single-screen (manual?) level design. A very simple platformer layout.
Players are moving/jumping around while eggs fall from the sky, and they obviously may not hit the floor. Keep them up, keep them from breaking, as long as possible.
Even though this is just a sliver of an idea, I marked it quite high in terms of potential because, well, I think this simple idea could actually sustain a full commercial game.