I actually had a similar experience. I never thought anything of the theme when I was playing the game, for some weird reason, but when I came back later to check the song out and learn it I was really hooked. It has a kind of Slavic or Russian feel, it seems to me, which I guess is appropriate.
You know, I would definitely like to see what you would do with Requiem for Lutz/Esper Mansion, since I know that's a favorite of yours, and it's just a really haunting song. But on the subject of Phantasy Star I, I can personally never get enough of the final dungeon theme. I would love to do a piano version myself, but I think you could do the chordal stuff and elaborate on the theme a lot better.