Ninja Gaiden is one of the most influential platformers on the NES, but the first thing someone should understand before playing it is that it doesn't actually abide by the sensibilities of a platformer. Games like that are typically about balancing speed and caution, with speed allowing you to clear longer gaps and avoid more enemies, and caution letting you anticipate the danger of hazards past your vision range. When playing Mario games, most people just hold the run button down by default, but this balance is the reason why Mario doesn't always move at maximum speed. It demarcates the two priorities you can have when traversing a level, letting you deliberately switch between the modes of reckless efficiency and safety. Ninja Gaiden’s buttons on the other hand are jump and attack, hinting that the two gameplay states aren't between caution in speed, but of speed and aggression. There is absolutely no room for caution here, taking any steps backwards will have enemies immediately respawn and kill you in seconds. How soon enemies respawn when you start backpedaling can make the game feel extremely unfair, but the level design begins to shine once you discover the flow among the hazards. When you need to make it to the boss and are effortlessly slicing through every enemy without pause, it gives you the unique satisfaction only great action games can deliver. I’ll add the parenthetical that there are some parts where I think the difficulty spikes into unfair territory, but for the most part I would say that satisfaction is worth the effort.