Ys I is showing some age, even with the new graphics, but it's still a challenging adventure and the music is fantastic. It's noteworthy that this is one of the few action games I know of that you can play from beginning to end with a single hand since there's no attack button and you just bump into enemies at a certain angle.
My biggest gripe with it are the dumb references some idiot added during localization. That's just disrespectful.
Ys II is a straight improvement over Ys I, the addition of a magic is a welcome one and the bosses are way more memorable. On the topic of presentation, the music and environments are outstanding as always.
The story also provides a satisfying resolution to the events of the first game and there are no ridiculous puzzles this time around. No more eating an apple so you can have a conversation with a tree that gifts you a sword.
Overall, I would say Ys I is great and Ys II is excellent. I totally recommend them. Also, if you are reading this because you want to get into the Ys series then you can perfectly start with the latest one if you want to, they are largely self contained.