I would make a game where the player character is a little kid. A short introductory story would brief you on your mission, which is to defend the monkey bars. Against a horde of monkeys. Many of whom are wielding monkey wrenches.

There should be a good variety of tricks, tactics, and techniques available for fighting the monkeys, and there should also be some more diplomatic options as well.

The graphics and the base game could be quite simplistic, but there would be room for as much embellishment as you have the time and inclination to do.