If you are interested in game design, the vision statement for the game is a jewel in itself.
Here is a link:
(CONTAIN MANY SPOILERS)http://www.rpgwatch.com/files/Files/00-0208/Torment_Vision_Statement_1997.pdf
This is what happen when the designers are genuinely excited about the game they are making.
Holy crap this thing is funny. It's so '90s it hurts, but it's clear they loved tossing ideas at the wall. Pity technology wouldn't let them do everything.
Tiling is for bathrooms, not games.
"Fireball" can go hide in the fucking corner when you unleash your arsenal.
Equip gnarly stuff. (Seriously, when was the last time you heard someone say 'gnarly'?)
"The best part about Ultima 7 was that you're guys were always hungry. Nothing like spoon-feeding your companions to make you feel like a hero. Hellloooo, fun!"
Forget fragile elves, rock-humping dwarves, useless hobbits and with them, the mind-numbing boredom of every RPG ever released.
To be honest, a lot of modern developers should read this too. It would do them good just to remember what raw enthusiasm used to feel like.
I think the deviations from the vision statement were intentional rather than mandated by technology. It makes the game seem like a much more conservative project than what was produced. The finished game seems to be far more nuanced and cerebral than what was presented.
I'm still in awe at the game. I think that one of the biggest things is it's holistic approach to storytelling. While Bioware RPGs tend to be written as a sequence of unconnected scenarios by different teams, PS:T was planned almost entirely by Chris Avellone.
The other writers were pretty good too, as the quality of the writing is high throughout. Replaying PS:T always makes me sad that voiceacting killed game writing.
As for means of acquiring the game, it's up on GOG.