Planescape: Torment and Baldur's Gate II are the two best AD&D-based PC-RPG's ever made.
EDIT:
Planescape might BY FAR have the best prose ever written in a game period (and will probably never be duplicated, since games rely less on prose b/c of amazing graphical improvements and advancements over the years AND also b/c of the new rule that for some reason EVERY line of dialogue has to be voice-acted). Planescape also has dialogue-options galore for quests w/ multiple outcomes (and very deliberate about these decisions), but BG2 has some of the best strategic-RPG combat around. BG2 also sports much better storytelling and writing in comparison to its (awesome) predecessor.
And yeah, BG2 has some awesome characters and storytelling moments...
Yoshimo turning on my party was CRAZY and quite unexpected.
Regardless, everybody who loves RPG owes it to themselves to play both of these masterpieces.
EDIT 2:
Oh, BG2: Throne of Bhaal is probably the most epic expansion pack ever made - PERIOD. That game could've easily been called Baldur's Gate 3.