significant improvement over the previous entry in every way; far less annoying enemies and other obstacles (some notable exceptions), far more consistent behavior where it matters, much better sprite work and overall aesthetics, much better music, etc. just holistically far more pleasant.

the first game had an issue a lot of games of this generation had wherein many enemy and especially boss encounters are either trivial or absurd because you can't realistically dodge their attacks. due to that, the dominant strategy -- at least given the limitations of most human beings -- is just tanking damage and shooting the enemy hoping you win. most of the bosses in Mega Man 1 require this "strategy"; some still do in 2, but it's much less. enemy behavior overall is also less buggier and more predictable, which in a similar vein allows for more neuron-activating tactical decision-making instead of mindless spam. these are all sort of "platformer 101" elements, so it's hardly high praise and compared to contemporary offerings this game still isn't very special, but given the quality of 1 noting these improvements is relevant.

also weirdly... profound? the [famous] intro, some of the levels, combined with the [famous] ending, are all very emotional and evocative for what this otherwise is. i presume that's mostly the music working its magic; actually, the music in general is very good, able to capture a lot of tones (i.e. "vibes", not musical tone) in ways that contemporaneous games don't come close to. with this game one can start to see what people see in this series.