Do you still have your copy of Metroid for the NES? If so, does it still work? Whether it does or not, seeing NES Metroid in your GameBoy Advance isle will add some nostalgia with it's pixelated cover. This is a exact port of the original Metroid shrinked to fit onto the screen of the gba. On the original Metroid box it had the words "Password Pak" written on the cover since being able to save your game with passwords was a big feature back then. This Metroid update does have the same password system as the NES version, but also saves these passwords so you won't have to write them down or memorize them. The original Metroid started a new style of gameplay, that later Castlevanias got inspired from. It allowed players to freely explore the world without following one path. Samus can find upgrades, which will allow Samus to gain access to areas that were blocked off. If you never played the original Metroid, the Classic NES Series Metroid will save you the hassle of finding a working NES and a copy of Metroid.
Classic NES Series: Metroid Game Media
More Classic NES Series: Metroid found on this site