Don't worry too much if you're stuck. Taking a break can help tremendously. Go outside and play. Get your mind off it for a while and come back fresh.
Just remember less is more. First think of a simple, fun mechanic. You can go the 'physics game' route but I think this theme lends itself to a narrative (story telling) and maybe a twist on the visual novel genre. It could even be without visuals! You can make sound the whole game and play with the idea that the sounds (words or just abstract noises) are leading the player through the game.