From what I have heard from a LOT of people, I should really give Planescape Torment a go.

Add one more in that list of people. Planescape: Torment is the best RPG you can get on a pc. The BG series was very good, though not up to par with torment.

The story is very original, the game is very well written. It seems they had DMs on the design team.
You get quests, not your typical fedex quests(you know, go fetch this and bring it back then take this to this guy etc), but quests where you'll need to think. It's not like BG, you don't have to finish all quests to continue, and some you never will. Some quests you won't discover at all. The ones you'll solve, some you'll solve them right away and some after a long time. You can pick up any items you'll find, some of them might have something to do with a future quest or they might be totally useless. But you cann't carry everything with you. And you cann't be certain which items are useful. Sometimes, even garbage might be of some use.

You don't choose an alignment for your character, it chooses you. (soviet russia comes to mind) Depending how you play your alignment will form accordingly.

I could tell you alot more but I'll let you see the game yourself. As you probably realised, this isn't for gamers but for D&D players. ie. if you expect and demand to open every door, solve everything, collect everything and see everything there is to see, then you might be dissapointed. If on the other hand you are a D&D player and you've been dissapointed before by the rest of hack'n'slash mighty magic pseudoRPGs, then you're in for a treat with this one.

I've talked in the past with friends who finished torment and each one's gameplay and experiences was totally different.