There's a moment early in Mass Effect 2 where your character, the resurrected Commander Shepherd, answers a series of questions about the events that occurred in the previous game. I think what they're trying to do is remind you about those plot points so you won't be taken quite so much by surprise when other characters mention them later on--or, if you're a new player, establish a little context so it won't seem completely random. But because the writing is a little awkward, it doesn't come across as an establishing infodump. Instead, in a surreal twist, it sounds like the characters are participating in a kind of retcon--letting the player's answers redefine their past actions. I love this idea, and wish it wasn't an accident.
A retcon, for the non-fandom crowd, is a portmanteau word for "retroactive continuity," and Wikipedia (unsurprisingly) has a fine list of examples, ranging from Nero Wolfe's birthplace to the altered appearance of Klingons in post-Kirk Star Trek. The retcon is a tradition as old as humanity, but it's rarely invoked in a planned fashion--in part, because it's usually so clumsy. Humans are good at maintaining continuity in our narratives, and we don't take kindly to authors who break their own fictional rules unless they can do so very, very elegantly.
But in video games, we have a sort of special case. Often here (and specifically in the Mass Effect games), the player is in control of continuity to a greater degree than other media. Is Commander Shepherd a woman of principle, or a ruthless pragmatist? The player chooses between these two, or even mixes them on a case-by-case basis. You don't know, necessarily, what kind of person she is until the player makes that decision: does this Commander Shepherd approve of the Genophage bioweapon, or find it deplorable? Does she believe in killing mutineers? What about the murder of treacherous former allies? And if those answers differ, it's up to the player to mentally reconcile them as a coherent character, offering up retconned justifications as necessary.
So why limit this to just the character arc, when a virtual world could offer so much more? ME2's dialog misfire offers a glimpse into a game mechanic where dialog doesn't just define a character, it can redefine the events that led up to the current moment, or the world around the player's avatar (cross a gap by insisting that you funded a bridge, perhaps, or clear out dangerous animals by bemoaning their extinction). If I had the time to spend on personal coding projects right now, that's something I'd explore: a game where you can redefine the state of play just by verbally disagreeing with it. I think it could even be an opinionated statement, not just about the way we adapt stories over time, but also the power of rhetoric to effect change, and the subjectivity of human history.
Or maybe I'm just describing a pretentious version of Scribblenauts. Either way, surely it's an opportunity missed.