Metalgun Slinger is a Japan-only 2D platform game for GameBoy Advance set in an old-western Sci-fi world. The player controls a blue-haired boy who finds a special gun. The game is similar to Mega Man or Contra - run right, jump on platforms, avoid obstacles like holes and spikes, and shoot enemies. The player can slide into enemies, run and shoot simultaneously, but cannot shoot at an angle and run simultaneously.
The game features various levels, including ones where the player rides a bike with their friend or battles against bosses. One notable boss is a green-skinned mutant with a mohawk. As the player progresses through the game, they can upgrade their special revolver, which is the hero's primary weapon.