A place where nobody dared to go
At the time I only tried this game for a bit at a relative's house, but it did intrigue me. I've since beaten it via emulation and with a hack that fixes some bugs, and I think it's a decent sidescrolling Action RPG. It's got an unusual setting, some good music, good enemy variety and some neat touches like gear showing on your avatar and dialogue portraits. It is kind of cryptic though and it's possible to get stuck at one point, as well as a bit grindy (the keys which have to be bought, one at a time, as well as for gear and for levels). While the early-mid game is tough, the difficulty starts stagnating in the late game so if you can hold out for that long you should be able to beat it. In the words of the game: Don't have negative thoughts.
Fun fact: It's actually a spinoff of the Xanadu series, itself a variant of sorts within the Dragon Slayer series, and the most recent one was Xanadu Next from 2005. That game is more like Ys though and it's fully top down view.