For me, in a game, the writing, the themes, and how story/stories are told and how they unfold (the directing, essentially) are what are most important to me. Following close with that of course then are the strength of characters, the story itself, the lore, the atmosphere, and how rich/deep I am immersed in a creative world. The music and overall sound also matter a lot to me.
To me, Planescape: Torment is my favorite game of all time, the writing is phenomenal and the surrounding philosophical ideas focusing on being/identity, choice/morality, life/death, and all the other themes to be found, are unmatched in any game I've played.
in RE: to what has been already said in this thread:
I think there are a lot of suggestions for games that you might like that you are missing if you have a little more patience and gaming-ability than what I think these other suggestions are giving you credit for. After all, you have played Planescape: Torment, and even if you do as little combat as possible when you play it, you know what combat is like in it and have weathered it fine and come out the other side with having experienced one of the best pieces of art of the 20th century. Now, that's not going to happen with BG/BG2, but - especially if you put them on an easier difficulty setting - BG/BG2 have a great great story, with great characters, and a lot of great things in them that I consider them worth playing, absolutely, more than KotOR 1 or 2 even. The stories in KotOR 1/2 are very good, and you should play them, definitely, but the power of the writing does tend to lack more than the other suggestions I'm going to make (and to BG/BG2.) The characters, worlds (even though it is Star Wars)/atmosphere, and depth of story just aren't as great in KotOR.
Following that, The Longest Journey is, along side with PS:T, the other of the greatest pieces of story-telling in a game, ever, FOR ME. Again, because of the writing itself as well as the story and the themes which encompass it.
Jumping from there:
Before you even try BG/BG2, if you're going to give some "classic rpgs" a try that you want to get a great story from, play Fallout and Fallout 2 and then Arcanum, THEN play BG/BG2. Make sure you play all of the unfinished business content in all of these games (I guess I shouldn't assume that you've done so with Torment, even, so make sure you play all of that as well if you haven't.) I even recommend going ahead and playing with the mods (the ones that don't change too much, just unlock content/fix a lot of bugs) on your firs time through for them all.
From there:
Depending on how much you want to tussle with any of those games combat mechanics/systems and how long it may take you to eventually make it through any or all of those games (though really, you can just turn the combat difficulty down and breeze through, but the experience and effort you put in DO help the story pay off a little because of actually experiencing some of what the character's have to go through a little more) you may want to experience some other REALLY GREAT stories that other games have to offer. Try these:
Interstate '76 - Can you play driving games that have good physics and aren't complete arcade-style? Do you like to? Even if no, I think for this game you could like to. While this game is a car-combat game at its core, once you get a feel for it (it has a learning curve for driving and shooting targets, but once you get the hang of it, it is KILLER FUN, some missions can be hard even then, but again, you can adjust difficulty level), it is seriously one of the best games EVER. What makes it that way? Aside from its unique game play that I find addictive and extremely cathartically satisfying, it has all of the fore-mentioned crucial characteristics: great writing and directing unfolding a great story with great characters in a rich atmosphere accompanied by one of the BEST soundtracks ever in a game.
System Shock 2 - Again, a different type of game, it sort of plays like a kind of FPS, but it's not good to think of it as a FPS at all. It has inventory, character customization with leveling and allows for different play-styles (stealthy vs. gun-blazing, with a bit of variability.) Again, a really great story that is written and unfolds very well, the voice-acting is superb adding even more to the atmosphere that is one of the best ever in a game.
There's others with very good stories, The Witcher series, Gabriel Knight 2, and about a dozen other adventure games that all are worth while if you like a good story. But that's enough for now, I need to go make lunch!