Temple of Elemental Evil because of tactic style D&D.
Baldur's Gate 2, Icewind Dale 1 & 2 - great, old style stories.
Planescape Torment - splendid companions and protagonist.
NWN 1 - lots of modifications and Deekin.
Witcher 1 & 2 - Games that contunue books.
Arcanum - clever combination of...