"Don't copy that floppy!"
I hear you can install the games on the HD. I was too young to understand how the X68000 worked and everything being in Japanese didn't help either. hehe. From what I read, some games could be installed on the HD if it supported it. Of course back in that time (Amiga/Atari ST time frame) HDs were very expensive.
I hear there's a really nice version of Ys I (and II?) on this system that looks great. Probably has some really good music too. There's also a ton of arcade ports to the X68000. A really interesting machine to say the least.
The only Ys games there are for X68000 are the following:
Ancient Ys Vanished X68000 - A beautiful version of YsI. Dempa Micomsoft / S. Senoo worked on this for two years, and the result is simply amazing. It also features two exclusive tracks: "Mura" and "Mountain Road", both composed by "GORRY".
The game has some damn fine artwork drawn by none other than Yoshitaka Amano! The manual has a textured cover and is just amazing.
Then we've got YsIII - the best version of all. Developed by Falcom. Excellent graphics and excellent music. The gameplay beats all the other versions.
Oh, and then there's True-Ys and True-YsII. Unofficial ports of the PC-9801 versions. Ported (illegaly) by "TEAM MILKHOUSE". YsI has an added sound test where you can hear the unused songs of YsI. Both versions also feature a much nicer font, so it's easier to read the text.
That's all there is. Dragon Slayer VI: The Legend of Heroes also got ported to the X68000. I don't remember which company that did it at the time. It might have been T&E.
(Dragon Slayer I was also released on the X68000, but that's not very interesting, now is it?)