Nintendo had been having a lot of early success with their launch titles and their own made titles released within the first year of the NES' life cycle.
Metroid was one of those titles. It was released by Nintendo in 1986. Metroid used the same engine as Kid Icarus, but focused more heavily on exploration. Instead of linear platforming like Mario, players were given a huge map to explore as Samus. It drew heavily from sci-fi horror at the time, like Aliens.
The game could be beaten with the standard equipment, but it was a challenge. The idea was to explore the map all over and find all the hidden items and weapons, as some areas could only be accessed with certain items. Still to this day, it is considered to be one of the best games in the NES library.