Sick game and a great start for the series. I know it's a staple of Mega Man, but I still have to say how getting past each Maverick in your own order and finding out how to take on them is really entertaining and lends itself to tons of replay value. The music is simply amazing all around.
The last stages can be quite challenging, but rewarding. My only issue with them is that they're a little awkwardly paced with the bosses, especially when I compare it to the sequel. The final boss was also very difficult, and defeating him was so absolutely satisfying that I cannot quite express it with words.

Great game and I don't think it has any meaningful enough shortcomings.