"Metroid" was one of the first non-linear video games. This means that it did not force players to play through the game in one way. Players could explore and go to all of the areas in whatever order they wished. The basic gameplay is a mix of adventure, platform shooter, and action. The player controls the main character Samus while exploring the game's cave-like environment. Because Samus starts only with a weak attack and a short jump, players must find power-ups to make the attack and jump stronger, in order to get to new areas of the game. While there are many different small enemies that players meet, there are also large bosses who must be killed in order to reach the last level of the game.