Space Wrek

The player controls a spaceship which moves in all directions, and can fire vertically upwards or downwards. Gameplay takes place within a series of nebula which can not be shot through. Each level has a red ship that wanders randomly off the screen, multiple blue ships that encircle a vortex, a large planet with a single benign ship attached to it, and 3 green saucers that fly about at random. The goal for each level is to destroy all enemy vessels, and when this is accomplished, the player progresses to another identical level. The player's is tasked with protecting the city on each level, but only one structure can actually be destroyed, and the enemy AI prevents the other buildings from ever being hit, making the entire issue of city defense moot. The player starts with 3 ships, but gains an addition ship when a level is completed. If all ships are lost, it's game over.