e (Melee)

This is an extremely underrated game, there is especially a lot of hidden depth when you learn how to access the hard mode where you die in one hit (the deaths only put you back to the beginning of the screen unless you game over). You can switch between different characters on the fly, each with a different bullet types, which can help with the constant interesting and different challenges the game presents to you. The final level is a culmination of all of those challenges and has you using all of the different characters. There is even an epic side-scrolling schmup section. The visuals and music of the game are all beautifully crafted as well. Very satisfying experience and well worth playing. All around one of the most solid NES games ever made, rivaling even Megaman 2 IMO.