I didn't see a topic for this series so be it !
YS is a series of Japanese A-RPG who take place in an alternate Europa. The name come from the French myth of the city a Ys.
First of all, the PC episodes will certainly never be on GoG because they have never been translated officially (but You can easily find fan-translation across the web)
The main protagonist in the series (expect Ys Origin who has never been translated) is Adol Christin, a redhead warrior. The plot is not the reason to play to Ys. You play to Ys because of his excellent gameplay (thought it's quite special for the first two episode) and his awesome music !
The episodes are more or less independent except the I,II and IV who are directly linked.
And like I said before the musics are the definition of epicness :
http://www.youtube.com/watch?v=bTZf-H4Rl3A
http://www.youtube.com/watch?v=HplgXxaKu5c
http://www.youtube.com/watch?v=GwlMSrzeolg
http://www.youtube.com/watch?v=6xL3qBb2RdA
http://www.youtube.com/watch?v=yICmlXlqKLM

PS : English is not my native language so point me if I made some mistakes.

Actually, Falcom sells some of its PC back catalog (including Ys) digitally through several distributors, like this one. Those are not quite GOG prices, but at least the games are DRM free too.

Picked up the 1 & 2 combo (Chronicles), The Oath in Felghana (3), and Seven all Collector's Editions for the PSP. Plan on making my way through them soon.

There is an RPG on that digretto site called Dinosaur. That is so awesome.

EDIT: Do any of those come in English? The screenshots for some of those games look really fun.

Unfortunately the PC Ys games were never officially released in english. There have been fan translations (exceptionally well done, too), but I don't know if they work with these versions.

And yeah, they're extremely fun games.

There is a couple of free english versions still available from Falcom:
http://www.falcom.co.jp/monarch/index_e.html
http://www.falcom.co.jp/vantage/index_e.html