Planescape: Torment took the somewhat cumbersome structure of the dialogue tree and turned it into a tangled dodecohedron of wonder within the wierd. While in many ways it refined tropes and technology from the tradition of Baldur's Gate and Fallout, Torment's approach to storytelling transcends its form, providing characters that unveil through interaction like layers of an onion, and a setting just as mysterious and complex. Every named NPC would have some bizzare-psuedo quest to unleash, replete with brilliant writing and EXP. From a nation of undead haunted by cranium rats, to a brothel of intellectual lusts, to a pile of skulls in the first of nine hells, Torment's setting breathed with just as much character as its core NPCs. Whats most innovative about Torment, however, is its abondonment an empty vessel avatar for a layered, complex character identity the player could explore through play - though the Nameless One was something of an empty vessel on his own, one found. What can change the nature of a man? Great role-play design, thats what.
-Patrick Dugan, True Vacuum
I'm torn between Planescape: Torment and BG2: SoA. I would nominate Planescape: Torment; not only because it still represents the best-written and most engagingly populated role-playing game I've played to-date, but because it was one of the first adult role playing games ever made. By adult, I don't mean that it contained restricted or child-inappropriate content, I mean that it looked at important issues of morality, guilt, and atonement in a serious and "adult" way. Most previous games in the genre turned around the semi-sociopathic "kill stuff and sell their gear/bodyparts to get cash to buy more stuff while engaged in your never-ending quest to save your girlfriend/people/world."
-Adams Greenwood-Ericksen, Institute for Simulation and Training
Again I have to praise Planescape: Torment, for many reasons. Among them are the fact that it broke away from traditional subject matter, had an deep, involved storyline, and allowed players to solve puzzles in various ways including non-violent solutions.
-Meg Haufe, Sony Online Entertainment
It's gotta be Planescape: Torment. Why? Simple: ROLE PLAYING. Baldur's Gate 2 had "epic setting" nailed, the two Fallout games take the crown for non-linearity, Neverwinter Nights had its unmatched online implementation, System Shock 2 probably tops the "successful innovation" stakes... but for going back to basics and getting the most important thing in a single-player RPG - the writing - absolutely bang on, nothing else is in the same league. I guess it's something of a sad commentary on the genre as a whole that I'm considering that a "quantum leap", but there you go.
-Matthew Woodward, Cambridge University