Cool, the only Ys I've ever played was the very first on the Sega Master System (and not that much) and the series has always been on my radar.
You should play the rest - its a great series.
Story isnt as strong as a Final Fantasy but the gameplay and music is great.
I played and finished so far....
Ys Origin (Steam/PC)
Ys I (Steam/PC)
Ys II (Steam/PC)
Ys Oath in Felghana (Steam/PC)
Going through Ys VI Ark of Naphitism (Steam/PC) right now.
I'm thinking about double dipping Ys Origin on PS4 in the future, its a good price tag (I think the lowest last sale was $7.99).
Going to get Ys Seven and Memories of Celceta on PC during the summer sale or winter sale later this year.