In 1993 there was a game called Betrayal at Krondor, sporting an huge 3d world and very deep rpg mechanics. BaK took place in Midkemia, the world of Raymond E. Feist's Riftwar novels. It was simply amazing, a very good mix of 3d exploration, turn based fights and a lot of clever puzzles.
Then Sierra lost the rights and had to thrash the idea of making a sequel, the development team did instead a new rpg with the same engine, called Betrayal in Antara. After a year Sierra took the rights on R.E. Feist's novels back and a proper sequel to Betrayal was made. Return to Krondor was built using a new engine that mixed pre-rendered backgrounds with 3d characters, giving the whole game top-notch graphics. They also added complex and very cool alchemy and thieving mechanisms, it's possible to brew and quaff custom potions and there's a fancy lockpicking minigame.
As storytelling goes, the plot is fairly linear but very well made, it's a game totally worth his price even today, and if you even tried Betrayal at Krondor you'll surely fall in love with this one as well.
I really hope to see both Krondor and Antara very soon on Gog.com too!
I remember that Sierra released BaK free for a limited time when Return to Krondor was released and it's why I know both games :)