Terranigma (SNES, and totally awesome )
Chrono Trigger (SNES, and a bit more awesome)
Knights of the Old Republic (XBOX & PC)
Jade Empire (XBOX, combat gets boring though)
Deus Ex (PC, RPG/FPS hybrid)
System Shock 2 (PC, same as above)
I'm guessing you've already played the FF series, or that other people are going to mention them, so I left them out of the list. I hate FFX though.