I always loved this song since the 1st time I heard it.
It sounds mystic, celtic, and yes also medieval.
I find it has this kind of flavour you can find in "mystic-celtic-new-age" type CDs.
I love the alternance of minor/major flavour, and the melody is superb imho, although I know it's reminiscent from old folk classic tunes
When I listen to it, it brings me serenity, tranquility.
I don't think I am old (I' m 43, I guess from the same generation as many people here), but I always loved music from older generations than mine...
I think that music taste comes from many things : mood of course, but also education, social context, what your parents were listening, people you meet in your life, etc...