Sequels that made a series

[Melcadrien]

Strange enough, I would say Mega Man 2.

The first one, in my book, was a bit of a mess. Not only that but if I remember right no one could progress in the wily fortress without the platform weapon.
It was when the second one came out where it truly shone. And the future Mega Man games followed suit.
That and I loved the music of Mega Man 2, especially the first 2 wily stages.