Although true color (as opposed to a colour overlay for a game that was otherwise black and white) began appearing as early as 1975, Galaxian took graphics a step further with multi-colored animated sprites and explosions, a theme song, different coloured fonts for the score and high score, more prominent background 'music' and the scrolling starfield, and graphic icons that show the number of ships left and how many rounds the player had completed. Galaxian was very successful for Namco and introduced several 'firsts'. The player defeats one swarm, only to have it replaced by another more aggressive and challenging army in the next screen. The ship can only fire sparingly by default, with just one shot on screen at a time, but rearmed instantly when an enemy is hit or the shot leaves the top of the screen. Swarm after swarm of alien armies attacked the player's ship that moves left and right at the bottom of the screen.

In contrast to Space Invaders, however, Galaxian adds an element of drama by having the aliens periodically make kamikaze-like dives at the player's ship. Like that earlier game, Galaxian features a horde of attacking alien armies that exchanged shots with the player. Galaxian expands on the formula pioneered by Space Invaders.