I recently had the opportunity to watch this: (it will be disturbing, so don't watch it if you think you might be too sensitive)
 
  
It's the very uncomfortable scene you may have heard about from Call of Duty 6: Call of Duty 4: Modern Warfare: 2 .  I thought it was disgusting and I was physically sickened.  Which is great.

In film and writing, artists are often well received when they try to do this to their audience.  Hotel Rwanda was horrifying to watch because it put the audience in a place it doesn't want to be: in the middle of a race war, with characters who see some terrible things.  It shouldn't be shown to sensitive, young children, but to not watch it because it's not enjoyable is to miss the point.
 
Along comes Modern Warfare: 2, in which, for one short mission, the player has to assume the role of an undercover operative in a terrorist cell.  Along with your terrorist buddies, you have to shoot your way through an airport full of disturbingly realistic fleeing civillians.  After watching the video (I haven't played it and don't intend to - apparently the rest of the story is about as deep as Diehard 4.0 and no Call of Duty demos have appealed to me in the past), I was left with an appreciation of how terrible such an event could be, and how difficult it would be to do such a thing in real life.  There will be a few Daily Mail readers who will put this in the GTA IV box of games that make mass murder fun, but I think this is the most salient statement of how evil such acts are I have seen in gaming.  It discourages me from going on a killing spree as much as Elephant.
 
As it's an FPS with a fairly quiet protagonist, you can't hear your character's dispraise of the events, or see his facial expressions.  Also, due to the nature of games, to some extent, the player has the power to minimise or maximise the destruction - go for knee shots or shoot them as they try to crawl for safety.  This leaves very little of the outcome in the players hands though - the other terrorists will kill plenty without your help and stopping them will (I assume?) result in failure.  So, despite this vignette being interactive, the conclusion the interactor is supposed to make is clear - "this is a tragedy and these are some evil people".  It says something to me about terrorists in the real world and in the wider context of the game it tells you something about the antagonist.  Being in his shoes lets you know what an unfeeling shit he is - that he can do what you just did and still talk in that calm, cool voice.  The judgement passed in voiceover beforehand, and the sad string music near the end leave no option for "tee hee, killing is fun" to be a valid interpretation.
 
I gather the rest of the game is more traditional soldiers-shooting-bad-guys fun, but it seems Infinity Ward are experimenting with storytelling in a mature way.  They have to make a big dumb action game to sell units, but being guaranteed millions of sales through the Call of Duty brand, Activision's marketing and their ability to design good games, they can insert an experimental bit that any less well-positioned developer wouldn't get away with.
 
It's a sign of a mature medium that it can be used for something other than pure "fun" entertainment, and I hope other developers will expand upon this idea and bring us new "non-fun" games that do similar things to dramatised accounts of historic events in film.  Imagine playing the role of the UN peace-keepers in Hotel Rwanda - wouldn't being in control make you so much more angry that you can do very little to stop the killing?  In the next level you'll be a Hutu soldier gunning down the enemy and beating civilians.  These levels will make you appreciate the injustice of the situation before you're finally put into the shoes of a Tutsi rebel, fighting back and feeling the rush of getting justice.  But ultimately, the Tutsi win is bitter-sweet because it comes after a hundred days of genocide, during which a million people were killed.  This game would be about as fun as that level in Modern Warfare 2, and it'd make you do some terrible things to civillians (hopefully in a less cartoony manner than GTA) but it could be a vignette of human evil as powerful as Schindler's List, made even more disturbing for the audience because they are active.  We have plenty of World War II shooters, but no Schindler's List; a few Vietnam games but no Platoon*; plenty of games about the challenge of shooting a gun, but very little that deals with the human cost surrounding conflict.
 
*Well, there is this.