The Metroid series contains gameplay elements from shooter, platformer, and adventure games.[3] The series is notable for its non-linear progression and solitary exploration format where the player only controls Samus Aran, with few or no other characters to interact with. The series has been a 2D side-scroller in all its incarnations until the Metroid Prime series changed the perspective to a first-person perspective, leading to a new first-person shooter element. The player gains items and power-ups for Samus's cybernetic suit primarily through exploration, and occasionally by defeating alien creatures through real-time combat with the suit's arm cannon. Many such upgrades enable further avenues of exploration.[3][42] A recurring upgrade is the Morph Ball, which allows Samus to curl into a ball, roll into tight places and plant bombs.[3]
The original Metroid was influenced by two other major Nintendo franchises: Mario, from which it borrowed extensive areas of platform jumping, and The Legend of Zelda, from which it borrowed non-linear exploration.[3] The game differed in its atmosphere of solitude and foreboding.[3] Metroid was also one of the first video games to feature an exploration to the left as well as the right, and backtracking to already explored areas to search for secret items and paths.[4]