Former GameSpot executive editor Greg Kasavin has kicked off a "Truth, Love, and Courage" blog (the name of which is inspired by the virtues instilled in the second Ultima trilogy), and one of his first articles is a retrospective for Black Isle's Planescape: Torment. Reading about my favorite RPG of all time never gets old:
In other words, Torment is the first RPG to introduce player intent into dialogue, which may be contradictory to the substance of the dialogue -- it's a game in which you can say one thing and mean another, and use this to deliberately lie at times, by means of the authored choices presented to you.
In a typical RPG, you might be asked by a character to retrieve an item, and tell that person "Yes, I'll do it" even if you as a player don't really know if you're going to do it or not -- probably you just want the quest logged in case you stumble upon it. You don't think about these types of interactions, and, as evidenced by the completely disposable text content for quests in games like World of Warcraft, they do little to build a meaningful connection between you, your character, or the gameworld. But in this same type of situation, Torment typically would give you at least two options: "Yes, I'll do it" (Truth) and "Yes, I'll do it" (Lie). And it would fully support these choices -- lying would affect your character's moral alignment, leading to other changes in gameplay. But even when it didn't really matter whether you told the truth or not, the game made you stop and think about what you were saying.