Sequels that made a series

[gamemaster1991]

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.

Strangely I have to disagree with you. Sure Mega Man 1 was basically crap and Mega Man 2 was better as a whole, I find Mega man 2 to be still lacking. The Robot Masters are all classic, the music is the best in the series, the Metal Blades is the best weapon ever, ECT. Ofcorse but IMO the game is way to easy (a side from the pain in the ass that is Quick Man's stage and the Eye Laser boss) and The weapons are too unbalanced. The first time I played it I loved it, but the second time I though every single boss either without getting hit or by getting hit once or twice. When fighting a boss (or going though the stage), it normally comes down to "do I use the Robot Master's weakness, the Mega buster, or continue to use the Metal Blades like I have all game?". If I remember correctly, there are only three bosses that can't be hurt by the Metal Blades and that's Quick man (Time Stop + Crash Bombs), the Eye Laser boss (Crash Bombs) and the Final Boss (Bubble Lead). The games are meant to be a Rock-Paper-Scissors style of game where you find the best weapon for each one boss, and when you only need one weapon for most of the bosses, it really doesn't work.

IMO Mega Man 3 and 4 are where they got it right.