You need Metroid II: Return of Samus
if you're a completionist. After all, this Gameboy adventure tells the story of how Samus Aran met the baby Metroid - Setting us up for Super Metroid and Metroid: Other M.
Heaven help you if this is your first Metroid game, though, as it can seem impenetrable. You're dumped in a location (Platen SR388) with no idea as to where you go and no map to guide you on your mission to shoot down 39 Metroids.
It doesn't help that the black and white visuals mean many locations look similar and you may struggle to work out where you have and where you haven't visited. On the flipside however, these monochrome backgrounds do heighten the feeling of bleak isolation and desolation for which the Metroid series is famous for. Whether intentional or not, this apparent limitation of hardware serves as a boost to atmosphere.
Once you get to grips with Metroid II and have broke through some of the secret passages in the walls, you'll find that it has more to it than most GameBoy titles.
With some great power-ups to collect, including the Space Jump, Plasma Beam and Spider Ball, this is an enjoyable game that isn't just for hardcore fans. However, Metroid newcomers will find it less than welcoming.