A game where you manipulate a vector and try to maneuver yourself through a series of quadrants to locate the x-intercept of the diameter of a rhombicosidodecahedron. Or you could make a generic cactus simulator.

A text-adventure about you wondering what kind of game you want to make?

A platformer about saving a mushroom, just for a change.

I giant fire breathing turtle that has to save an Italian plumber from a princess.. Hang on...

Kirby Game. :p