
It's so good and so fondly remembered that people have turned it into an actual song called "Omoide wa Okkusenman" with different versions, like in violin form and a cappella.
One of the best Mega Man songs, and the one most likely to be recognized, is Wily's Castle Stage 1/2, from Mega Man 2. Megalomania's remixes of Quick Man, Flash Man, and Wood Man are pretty amazing. The intro starts it off quite nicely, and will probably be the one most people recognize as the 'Mega Man Theme' (aside from MM3's intro or Wily Stage 1 below). And the remastered version for Shadow Devil in Mega Man X5. The Wily Boss theme, a frantic and chaotic fight theme. You want a great remastering? Check out Mega Man 1's 8BitStereo. Powered Up's rendition of Wily Stage 2, a delightfully ominous prelude to the final battle. Made even more awesome with the version from Mega Man Powered Up. Wily Stage 1, A dark, somber (and, quite frankly, underrated) song perfectly fitting such Nintendo Hard levels and their cruel master.
Fire Man - Arranged, but the original is quite awesome indeed as well.Bomb Man is one of the most underrated tracks in the series.