There are two NES games that stand out in particular for having such great soundtracks, I still play them mainly to listen to those scores, in their original NES sound quality.
I'm talking about no less games than Mega Man 2, and Mega Man 3. It's amazing how the composer (whoever it was) managed to turn the heavy sound limitations on the NES into his advantage like that.
And they're pretty good games as well.
I rate Super Mario World above SMB3, but not by that much.
The Lost Vikings for SNES is one of them games one might have overlooked. But you shouldn't.