Back in the NES era, the late 80s and early 90s, there were two different types of games. Call them linear and non-linear. The linear games, like Super Mario Bros. and Ninja Gaiden, had you go through each level once and only once. The non-linear games, like Zelda and Metroid, allowed for backtracking and exploration. It wasn‚Äôt often you‚Äôd find a game that did both.