Gahh, no-one has mentioned the highly influential Ultima series, particularly Ultima's 4-7, Serpent's Isle inclusive. If you're looking for a game which is isometric like BG, optionally party and solo based, set within a large world of interactive characters with wondrous narratives, then look no further. In my opinion Ultima VII: The Black Gate practically set the benchmarks for this style of game.
Sometimes it pays to look backwards than forwards.
I can also third and fourth the reccomendation for Planescape Torment. It is indeed a literary masterpiece within the confines of a digital gameworld. Immersive, emotional, thought provoking and simply compulsive playing - but is definitely much more dialogue driven, in the tradition of Ultima and not for everyone.
There's also the final infinity engine related game, Lionheart - but I can't vouch for that too much, not having played it. Many say it falls apart by the conclusion. One other that comes to mind for similarity is Arcanum, which I also haven't played yet...
Cheers,
CD
P.S:
If anyone wants an original copy of Planescape, I have one spare for a possible trade. Feel free to PM.
[ 07-28-2006, 04:13 AM: Message edited by: CerebroDragon ]