It's a motorized model of a classic video game - Pong. Fully playable.
The game is played by two players, each of them have a paddle on the right or left side of the screen. There's also a ball that flies around the whole screen, bouncing off the sides. The players need to move their paddles so that the ball never reaches the left or right side of the screen. If that happens, one of the players scores a point. The machine counts and displays points automatically. When a player scores 5 points, it displays the message "YOU WON!" instead of how many points does the player have.
The model uses only 1 electric motor.
I built it because I wanted to make a Ping-Pong like game of LEGO, not on a computer.
I think it would be a good set because:
It's fun to play it,
It has a complex mechanism inside (contains more than 90 gears),