Hundreds of hours of gameplay, most of it excellent!
The original Phantasy Star is just as engaging in its own way as Final Fantasy (NES) was. Good characters, a good story, and a lot of variety in numbers and types of monsters. The bosses are all a little simplistic and they aren't of the cackling-evil variety found in the FF series. Get used to finding your way around mazes (a FAQ comes in handy).
Phantasy Star II is a tough game, but very interesting and with odd, likeable graphics. It is very linear in its layout, but levelling up takes a long while and a lot of patience. The weapons and armor chart that comes with the game is almost indispensable in figuring out when to upgrade, whether it's worth the money, who can use what item (frustrating). All in all, a fun ride.
Phantasy Star III - This is a fairly long game, as RPG's go, but most of it is spent changing characters as time passes, and there's a lot of walking and boat rides involved. Not for the faint of heart, and a walkthru is almost mandatory or you could end up wandering around for a long time. I can't say I ever developed a great love for this game, but it didn't suck.