Galaxian expanded on the formula pioneered by Space Invaders. Like that earlier game, Galaxian featured a horde of attacking alien armies that exchanged shots with the player. In contrast to Space Invaders, however, Galaxian added an element of drama by having the aliens periodically make kamikaze-like dives at the player's ship.
The gameplay was relatively simple. Swarm after swarm of alien armies attacked the player's ship that moved left and right at the bottom of the screen. The ship could only fire sparingly by default, but rearmed instantly when an enemy was hit. The player would defeat one swarm, only to have it replaced by another more aggressive and challenging army in the next screen. A plain and repetitive starfield scrolled lazily in the background, nicely contrasting with the action of the game.
500Unofficial Galaxian - Comprehensive information about the arcade classic. Includes platforms available for play, technical information, and gameplay.