The game could be like a sandbox game like GTA but without the killing innocents and stealing cars.
As Jim you can travel anywhere around Earth and even travel to space and other planets freely. You can vist the planets of the villans and even chase down their spaceships. You'd be able to battle such enemies as Professor Monkey-for-a-head, Queen slug-for-a-butt, Bob and No. 4, Evil and Henchrat, Psy-Crow, Fatty Roswell and Evil Jim. On Earth you can explore the cities and area, even enter Jim's house. You can explore the Turlawk mall and buy special items and unlock features. Of course you can call a car to drive around if Jim's ship is damaged.
Also the missions you get are from such characters as from the Princess, Peter, Hamsternator, Snot and other characters.
So these are my ideas, I hope you like them and maybe they could be used in the game or for an upcoming Earthworm Jim game.