Metroid: Zero Mission is a remake of the original Metroid title for the NES. This title was released for the GBA after the success of Metroid Fusion. As an added bonus, after completing the game, the original Metroid game, NES graphics and all, is unlocked and can be played from the same cartridge.
There are many differences with the original game that make it significantly more interesting than a straight port. It is considered a completely different game, with most of the changes being made so that it fits better with the future Metroid games, particularly Metroid Prime.
- Most of Samus' new abilities have been incorporated into gameplay. From small things such as being able to crouch, to the Space Jump.
- The graphics have been completely re-done to take advantage of the Game Boy Advance hardware.
- The speed of the game is faster, in terms of movement.
- The password saving system has been replaced by a more practical cartridge saving system, but as a result, there is no "Justin Bailey" code that reveals a suitless Samus.
- An entire level has been added taking place after the destruction of Mother Brain, where Samus' gunship is shot down after she removes her suit, leaving her stranded near a Space Pirate base with only a gun capable of stunning. This level revolves around stealth & running away from the enemy, until she uncovers the more powerful Varia Suit, explaining the suit differences in the original Metroid and the Varia Suit of Metroid Prime and Metroid 2: Return of Samus.
- If connected via link cable to Metroid Fusion, a Metroid Fusion image gallery is unlocked.