Thanks, Red!
I'm planning on doing an Apocalypse game, where the player can choose all forms of destruction (Nuclear War, Flood, Earthquake, Asteroids, etc) but i haven't yet stopped to plan the details, to keep the player playing, as you said.
This is a huge problem, usually overlooked by newer game designers. With Unity and Playmaker you can make a fast "interactive system", but to do a "game", a lot more planning and dedication is needed.
Since I don't have someone to help me with art (my weak point) I keep on studying and doing these short "interactive systems" waiting for the right time to try for something more complex and playable.