The FM synths kind of require a mental adjustment because they weren't nearly as common in American systems. There's the Sound Blaster cards in early DOS machines if I remember right, but...

It's a dramatically different soundworld, as it were, from the pulse and square and triangle waves of the NES and from the orchestral sound of today's games. FM synths can be very difficult to work with - they really are synths. I'd argue that the sound engineers were more important than the composer was (at least, where there were separate sound engineers and composers) when it came to the literal waveforms reaching the ear.

In good hands, though - the results are fantastic. Sega's soundtracks are great examples. Others I'd recommend are Castlevania: Bloodlines, Warsong, Streets of Rage, The Adventures of Batman & Robin, Time Trax, and Light Crusader. FM synths require a lot more care to make 'em sound good than PSGs or orchestras - the latter of whom basically takes care of itself.