The Ys series has always been know for it's great music, and this game is no exception. I played this on the SNES, and that's also the version of the OST that I used here.
You can find a lot of different Ys III OSTs (and other games) here: http://downloads.khinsider.com/.
This has got to be one of my favorite SNES soundtracks; about every song is memorable and adds emotion to the game.
There's a nice balance between epic, fastpaced boss music, rolling dungeon grinding melodies and quiet, melancholic story music.
I especially like the instruments used in the SNES version, they give the soundtrack an unique feel. The drum's hihat and snare are sharp and crisp, and the bass is clear and deep.
It's worth checking out the different OST versions to check some different instrumentations of a song; but in the end I'll always prefer the SNES one, if only for the nostalgic value.