Geimos is an arcade-style space shooter where players control a spaceship that flies over different planets' surfaces, destroying incoming enemy units.
The game has two different modes. "Mode A" keeps the camera's perspective fixed, allowing players to control their ship's altitude while flying around the screen and firing two weapons. One weapon is for ground enemies, while the other is for aerial enemies. Players face off against a gigantic boss enemy at the end of each round, requiring several shots to defeat.
Mode B is similar to Mode A, but the camera follows the player's ship movements instead. This mode features a fixed target reticle in front of the player's ship to help with aiming their fire.