The 2D Metroid Series offer a perfect mix of platformer action, adventure and intelligent puzzles. While preceded by Metroid (1986) on the NES and Metroid II: Return of Samus (1991) on the GameBoy, this is the game that gave the series its distinct look and identity.
While Metrovania is a thing and inspired many great games for decades to come, it is Metroid and not Castlevania the game that immerses the played in an eerie, dreadful, inmense and most of all lonely universe. It’s close to the atmoshere created on Ridley Scotts’s Alien, a clear inspiration for the developers.
Have a look at “How to play retrogames?” if you don’t know how to play retrogames.