While the gameplay is pretty repetitive- explore, find secrets, kill metroids, repeat- it's really satisfying and establishes a mysterious, claustrophobic atmosphere despite its limited hardware. Samus moves and responds really effectively, and the spider ball in particular is really fun to explore with. However, the method of advancement is strange- kill enough metroids, and the level of the lava inexplicably falls, exposing new areas. Compared to the brilliant exploration system of Super Metroid, it certainly seems rather limited, but on its own merits it's a fun little game, and plays really well for an original Gameboy game.