I just finished a conceptual design work for a testing environment of Where-Is-My-Heart? I was thinking about the game-play a lot. How does the player win the game? Or a level? How about this: As a player you have to find the way to the heart balloon. As the player grabs the heart, the level is completed. At the beginning of each level, we could have a short sequence of events, that in one way or another make the player lose his heart again. A bird stealing it, a gust of wind, etc.
So the main objective about the game is to explore and find a way to the heart. Riddles would be about combining information from the different frames. So it is more a cognitive game than a classic platform game.