Together with Bart you have to save the universe from evil aliens who have encroached on the town. Armed to the teeth, you should go through all the levels and get to their huge ship and make it a diversion. 

On the way to it you will encounter many difficulties so be always on guard. Shoot accurately, collect bonuses and get the new weapon. Stroll around the city of Springfield where you can shoot all the enemies you encounter. Do not stop shooting to stay alive.