Galaxian (Namco set 2)

Galaxian is a legendary single-screen shoot-em-up that took everything that made Taito's ground-breaking "Space Invaders" so good, and improved upon it on every level. Each screen starts with a wave of multi-colored aliens moving left and right at the top of the screen; the aliens quickly break ranks and start dive-bombing the Galaxip (player's ship) - either in single units or in groups of 3 - dropping multiple missiles as they descend. All of the aliens need to be destroyed before the player can progress to the next wave.