Mega Man II is broken as all hell. Once you figure that game out, it's painfully easily. The Metal Blades pretty much make you invincible in that game.
That's where 3 excels over 2, the game is a lot more balanced.
I love Mega Man 2 with an unfettering, never-ending, fiery passion, but I admit that the bolded statement is true. Metal Blades are insane. High Damage, fire in 8 directions, take up a minuscule amount of ammo. Even my 10 year old self knew that, and when I played Mega Man 3 I kept wondering what the Metal Blade equivalent was. There's none, and that's a good thing.