I think it would be hard to do unless the game was some kind of sleeper hit or had little hype. Otherwise people would learn of it and change their expectations, yah?

Another game that comes to mind that does a similar thing is Contact for the DS.

MGS spoiler alertz.

that's a potentially interesting idea. the only game i can think of that comes close is MGS2. you initially play as Snake and are privy to everything he knows, but after the tanker ending, that trust contract is broken. you no longer are aware of what Snake is up to, and for much of the rest of the game, you're trying to find out what your "former self" was doing. of course, it's not quite the same because after that, you're not playing Snake anymore.

MGS3 also played with this contract in a very powerful way. i'm not sure if it was intentional, but i didn't really realize i was playing Big Boss until the very end. again, not quite the same because you no longer "control" Snake after the end, but splitting off that contract at the end had a great effect on me. it made me sympathize with his actions, even though i might not have done the same. (altho...MGS4 complicates all that even more beyond confusion...)

another game that comes close is Portal. throughout most of the game, you don't really know who Chell - your character - is. you don't know her motives or history. and near the end, GlaDOS says, "You are not a good person, you know." and that makes you wonder..."hmm..who is Chell? why is she here? is she a criminal?" so while it doesn't betray player-character trust, it puts that in to heavy question. really cool. it doesn't really affect gameplay tho.

i can't recall any medium period that does that. narrators in books are usually trust-worthy (although not always correct nor fully-aware), as they are in movies.

imagine if in Half-Life episode 3, Gordon Freeman suddenly reveals himself as a Combine secret spy or something. that'd be interesting...who knows

@tubatic: i didn't play KOTOR, but wasn't that a matter of amnesia? i thought your character him/herself didn't even realize his/her past. very cool, nonetheless.

braid is a pretty interesting case as well. it's hard to say whether Tim realizes what he's doing at all. ..what is it exactly that he's doing anyway?

@Stevesan

That's what makes that one in KOTOR especially interesting, to me. Since I was playing it mostly good up to that point, the reveal moment actually encouraged me to take my character down the dark path from there on out. It didn't necessarily break the contract, but it changed the terms, so to speak.