Galaga is a single-screen shoot-em-up in which the player controls a 'Fighter' spaceship and must defend the home planet against the on-coming hordes of alien invaders called "Galagans". The Fighter can only move left and right along the bottom of the screen.

Galagans fly onto the screen in a variety of formations before forming troop lines at the top of the screen. Once all troop lines are formed the Galagans separate and start attacking the player's Fighter in ones, twos and threes. The top-line Boss Galaga need to be shot twice before they are destroyed.

The Boss Galaga has a tractor beam that can capture the player's Fighter. A captured Fighter changes color from white to red and stays with that particular Boss until it is destroyed. The Fighter can be retrieved by destroying the Boss that captured it, but players must be careful not to destroy the captured Fighter itself, or that Fighter is lost. A rescued Fighter changes color back to white and links up with the player's current Fighter, doubling its fire power.

As players progress through each screen, the speed and number of alien attacks increases. Alien formations also become more complex, making the aliens harder to shoot.

Bonus Fighters are awarded periodically throughout the game, as players reach specific point values, as dictated by the 'Bonus Life' dip switch setting. Each enemy ship also has an assigned point value (see Scoring below).

The alien troop lines that form at the top of the screen are, from top to bottom: Boss Galaga (in one row of four), Butterflies (red/white bug ships, in two rows of eight, directly below the Boss Galaga), and Bees (blue/yellow bug ships, in two rows of ten, directly below the Butterflies).

In Stage 1, the enemies do not drop bombs as they fly onto the screen. However, they do so in most of the later stages.

From Stage 4 onwards, a squadron of special bonus enemies called "transforms" start appearing. They're called transforms because Bees will begin pulsating and move out of formation to change into these bonus enemies. They appear in the form of yellow scorpions in Stages 4, 5, and 6, green 'Spy Ships' from "Bosconian" in Stages 8, 9, and 10, and Galaxian Flagships in Stages 12, 13, and 14. After that, the three different transforms are repeated in the same order. Transforms are always worthwhile targets because they are not very aggressive and are worth more than the other enemies. If all three transforms are destroyed, extra bonus points will be awarded.

Galaga also features CHALLENGING STAGES, these consist of 40 Galagans that fly onto the screen in formations but do not drop any bombs. The object is to shoot as many of them as possible before they leave the play area. When an entire formation of eight Galagans is destroyed, bonus points are added to the player's score. If all 40 aliens are destroyed, players are awarded a special bonus of 10000 points.

Two new gameplay features Galaga introduced are :
1) Players are given the chance to double their fire power.
2) The game has a rapid fire (automatic firing) option, whereby the player simply holds the FIRE button down and the space fighter continues to fire at the Galagan army in bursts of two missiles each.

Galaga '88 is an updated version of the old favorite, "Galaga", with more invaders and more player firepower. Galaga '88 gives players a chance to once again repel the invaders from the Galagan Kingdom. One or two players can try their hand at fighting the invaders. This time the Galagans have four more allies, each with unique weapons and defenses that a player must overcome.

By destroying special enemies or obstacles the player can get 'items'. When a player has two items, they can warp to another dimension to confront more Galagan ships with new strategies. In the Challenging Stages (labelled in this game as 'That's Galactic Dancin'), the player shoots down as many invaders as possible as the Galagans dance to a waltz, tango, march or jazz tune.

The player selects single or dual ship power. The objective is to destroy all the Galagan foes in each of the 29 sectors of the galaxy, with each sector more difficult than the last.

Unique Features :
* More opponents. In addition to Boss, Goei and Zako, the original Galagan crew, Don, Nin, Ban, and Gan have been added. Each of the Galagans has a unique way of challenging the players.
* Different types of ships. Players can choose single or dual ships (if the game option is set for dual and single). When the player retrieves a dual ship from the Boss's tractor beam, it turns into a triple ship with ten times the power of a single ship.
* Challenging Stages. In the 'That's Galactic Dancin' stages, the Galagan invaders dance to a waltz, tango, Sousa march or jazz tune, while the player shoots down Galagans to earn bonus points.
* Warping to a new dimension. By destroying particular enemies or obstacles and capturing two of their items, the player can warp to the next dimension.
* Player challenge. Each dimension has different mix of Galagans with different strategies to be overcome.
* Win back captured ships. The player can win back ships captured in the Boss Galaga's tractor beam. When the player destroys the Boss, the ships are released. If the player retrieves them, the ships become dual ships if they were single and triple if they were dual.
* High Score Mode. Upon completing a game, a player can enter his initials if they are among the top eight scorers on the game.

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-coloured aliens moving left and right at the top of the screen; the aliens quickly break ranks and start dive-bombomg the player - either in single units or in usergroup of three - dropping multiple missiles as they descend. All of the aliens need to be destroyed before the player can progress to the next wave.

This was the first video game released with 100 percent of its graphics displayed in true R.G.B. color.

The third game in Namco's classic "Galaxian" series, Gaplus picks up where 1981's "Galaga" left off. While maintaining the same classic 'look' of its predecessor, Gaplus's graphics are a definite improvement over those of "Galaga"; the game's increased color palette and subtle use of shading making the attacking aliens look rather more solid.

Another enhancement over its prequel is in the addition of a player-acquired 'Tractor Beam'. In "Galaga", only the enemies had access to the beam; enabling them to capture one of the player's 'Fighter' ships (the player then had to shoot the captor to release the Fighter). For the sequel, however, the player can now acquire the Tractor Beam. This is achieved by shooting one of the alien formation's 'generals' - a visibly more colourful alien than its comrades. The Tractor Beam will then activate for a limited time and any aliens the players captures (up to a maximum of six) will dock alongside the player's ship for enhanced firepower.

One final yet important addition is in the movement of the player's ship. In previous installments, the ship could only move left and right along the bottom of the screen; in Gaplus, however, the ship can now move UP the screen - although only to the halfway point. This is important as the alien's aggressive attack patterns will often see enemy craft swirling around the bottom of the play area.

As with "Galaga", Gaplus features regular 'Challenging Stages', with benign aliens swooping across the screen for the player to shoot as many times as possible, in order to try and spell out a word and earn extra bonus points.