im thinking about picking up planescape:torment, since i never played it but i hear good things about it.
Absolutely, entirely loved Torment. It's probably still my top game of all time, and one of the only games that I have actually completed more than once, playing through from start to finish.
Ghills is right that the world is very dark - without spoiling anything (because it's the very beginning of the game), your character wakes up in a mortuary. As in, on a slab in the mortuary. Surrounded by corpses. And a talking skull.
It's also one of the text-heavier games I've played - and that's a good thing, in my book (no pun intended). At times you feel like you're taking part in one of those old Choose Your Own Adventure novels, but an incredibly well-written one with a very dark, but also very sympathetic/empathetic storyline.
I think generally you get the most out of the game if you play through as a high intelligence/wisdom character (so, probably a mage type), but that's not a major stipulation and you can play through as a brain-dead, ham-fisted simpleton if that takes your fancy. The dialogue will recognise that as well.
Overall: can't recommend it highly enough. It's on GoG and, in fact, is their all-time top seller. All-time. Top seller. And it's $7.