There're plenty of NES-era soundtracks I adore. Some are iconic, some are just fun, and then some are just so accomplished, despite being 30-second loops, that it's kind of hard to comprehend.
Faxanadu was an interesting diversion from the norm, based on "a mixture of Norse...and Japanese mythology with some derivatives of Eastern religion", so says WikiPedia. It had a cool "title" ranking system for each new level of experience you attained. The world seemed huge, too, especially for a young child, and so the task of beating it was monumental.
That...and the soundtrack was just unique and epic. The section with fog covering everything clicked with me and so I chose to kind of take that even further by musically adding a haze to the whole thing, a la one of my favorite tracks by Washed Out.
Source: Faxanadu (NES) - Fog, by Jun Chikuma