In 19xx Capcom created a masterpiece
In the first MEGA MAN game there was much promise - the non-linear level selection, the unique mechanic of stealing boss enemies' weapons and using them against the others, the bonus items that changed up your method of beating the platform challenges. There was depth, color, good music, and an appealing little Everybot hero. But it just wasn't fully-formed yet.
MEGA MAN 2 so perfectly encapsulates all the essential elements of the 8-Bit Mega Man franchise that these days it might have been named MEGA MAN 1.0 - it makes the original look like a beta test. This is the complete article.
Upgraded from 6, now you've got 8 enemy robots, each with a colorful, well-designed stage and unique musical theme. Truly, there's no 80's game soundtrack signature like the Mega Man Beat Box - those percussive, driving melodies that sent you sprinting through each stage. From those songs to the constant change-up of platform jumps to miniboss fights, enemies coming at you from sides, above, and below, MEGA MAN was about creating an energy as constant as its hero's mechanical high-speed jog.
And there was still a degree of rock-paper-scissors logic to the way the boss weapons interrelated to each other. Unlike the later games, where all intuitive order went out the window, with trial and error you could quickly develop a ritual cycle to take you to the all-important Dr. Wily stage.
The addition of energy tanks helped tweak the difficulty level down to a more accessible level, but the bold could still forgo them if they chose. The password system gave you that extra flexibility to take a breather and fight another day. The three numbered platform devices were a vast improvement over the glitchy Magna-Beam, and paved the way for MEGA MAN 3's introduction of Transformer Dog-sidekick Rush.
And besides the 8 stage bosses you had those oversized, colorful mini-bosses - who didn't feel a rush the first time a FLYING ROBOT DRAGON swooped up from below and started knocking aside the narrow ledges behind you? And remember the first time you walked through that final stage, no soundtrack but the evocative "drip-drip" echoing through the air, and watched Dr. Wily seemingly transform into a mutant bat-lizard right before your eyes? That's 80's Game Nonsense Heaven.
Last, and certainly not least, MEGA MAN 2 brought into the world the no-foolin' greatest auxiliary weapon in video game history - the Metal Blade. 8-direction flexibility, high-speed delivery, nearly infinite supply. Awwwwww yeah.
The challenge level is arguably too far reduced - it's a dim gamer who can't eventually conquer it, and having a game that anyone can beat used to be a BAD thing. And as goofy and fun as the game's enemies are to look at, there wasn't a whole lot of animation to them, or variety to their attacks. It just became a question of finding the proper gun then blazing away.
This is pre-Power Slide and pre-Charge Shot, also, so there's not a lot of depth to the old Blue Bomber's movements and tactics.
The Bottom Line
If you've ever wanted to know what all the fuss is about, start here.