Cosmic Raiders is a side-scrolling shoot 'em up similar to Defender.
Like in that game the player's space ship can move both left and right and there is also a radar showing the locations of enemies.
The game takes place in the alien sector Larkin and the player's objective is to defend a planet under attack while also collecting energy sources from an evil alien race called the Larkins.
In every level four bombs are dropped along with a number of fighters to ensure the bombs reach the surface of the planet. The objective of the game is simply to clear all the enemies and get the highest score possible.
For every two bombs destroyed an energy star that the player can collect will appear. By picking it up the player's ship is energized with an invincible energy shield. Once all enemies have been cleared from one level the game moves on to the next.
Before starting out it's possible to choose the number of players (1-4), number of lives (1-9) and the intensity of the game (0-9). Level 0 is the easiest one and the only one where enemies do not get harder as the game goes on. Each player can have a different intensity level.