Sometimes iteration is a positive for series, but sometimes it never got better than the start. While technically a remade port of the arcade release, the important thing is that the first Contra still utilizes its mechanics the best. All of the weapons have different applications you have to pick between on the fly, there's a genuine focus on platforming and the game has a near-perfect difficulty curve. Later run 'n' guns, especially the Contra series itself, would end up focusing on set-pieces more and more with time and had you wandering flat terrain just shooting right primarily, but not the original. If you want a near perfect encapsulation of challenging and fair design (in spite of its brutality) this is the way to go.