When I beat Ys I the game felt hollow, small not because that's what the devs wanted to do, but because of technical or financial restrictions.

Ys II is a bigger and more developed game. With more areas, more enemies, more ways to engage with the world, and better designed bosses. It still feels like there are a lot of gaps where the devs wanted to put more content but it plays more like an actual game and not a proof of concept. 

The difficult curve is way better done, for the most part. Regular enemies are harder in the good way, it's easier to do damage to them but they also pack a punch so you have to be careful, and bosses are interesting with new mechanics and challenging enough, with the final boss being the only exception.

In the first Ys, I literally grinded my teeth during the final boss and died to him almost 30 times, in this one I defeated the final boss in my first try and didn't even need to use the revive potion. 

I don't think you will ever have any problem with him unless you handicap yourself by not using the items the game gives you right before you fight him or by being extremely underleveled. I played both games on Normal.

The aesthetics are also an improvement from the first game, with beautiful graphics and good art direction, at least in the Complete Edition I played.

The story is nothing to write home about but I don't play this games for the story.

I wouldn't recommend the first one unless you just want to play the entire series like I'm doing but this one is an easy recommend for anyone who likes action games.

Just beat Ys II. It felt more like a full game than the first one