Joe, ys is one of the most fun games serieses, well, ever.. Think Zelda, but with a bit more action, a bit less equipment/puzzles, and overall -- honestly -- more fun. Imagine an RPG series with ONLY the fun elements and nothing else. Games like Landstalker and Beyond Oasis owe a lot to Ys.
Tons of info (this is also my favorite website on the internet, you can read the articles all day):
http://www.hardcoregaming101.net/ys/ys.htm
Until 2005, only the first 3 were out in America, but # 3 -- which is EXCELLENT -- was on the SNES, at least, and is cheap/easy to find.
Xseed is localing YS I/II, III, and the amazing VII for the PSP, in North america. And is honestly probably the only reason to buy a PSP... I and II are the Wii virtual console, too. And you can get the first 2 on the DS, as well..
But fuck all those, just get the PS2 game, YS VI: Ark of Napishtim. It was seriously one of the best games for the PS2, and I got it off of amazon for $8. You slash things and level up and go into dungeons and kill more things and level up. Imagine Zelda, again, but every time you kill things, you get more powerful. Simple concept but addictive as hell. Diablo-ish, I guess.
Look at these screens:
It is
so fucking fun. I played it non-stop, straight through, and beat it in 2 days. I think I beat it in 9 hours, so it's perhaps a bit short (then again, so are most games that people worship -- I beat Devil May Cry 1-3 -- yes all 3 -- in a few days, each one taking 2 hours max... Viewtiful Joe can be beaten in an hour and a half... so yeah), but it's seriously the most fun you'll have, for one playthrough at least, on the PS2.