Betrayal at Krondor was one of the greatest RPGs of its time, and highly influential. The turn-based combat system in it was very deep and new ground for western CRPGs, while the storyline was excellent and the game world was huge. It was also a very hard game... Dragon Age has nothing on it.
I played Quest for Glory and then Betrayal (both fantastic) and had no idea they both were what I would come to easily define as RPGs.
Return to Krondor was pretty good, though it wasn't as good or innovative as its predecessor. It also wasn't hardcore enough.
If I could get Betrayal on a mobile device like a smartphone, a PSP, or a DS, I'd love to play it again.