So Joystiq has been running a series of "questions to the pros" about story and games, and I contributed a few lines. You can find the comments here, here, here, and here.
Now one thing that I want to expand on is the nature of identity in a computer game, in particular a MMO. Games differ from books or movies in that protagonist is united with participant. This is not unique to computer games - this is something that comes out of its ancestor RPGs, and even the early days of wargaming talked about "The Rommel Syndrome" (that is, should you optimize your strategy for the game or invoke the strategy based on the generals involved).
The protagonist is the viewpoint character(s), and while the reader/viewer should usual identify with him/her/them to some degree, there remains a distance between character and reader. A definite case of separation between what the character within the fiction and the individual participating (by reading or watching) that fiction. In an RPG or MMO, that space blurs and disappears, as you are cast in the role of the character.
Suddenly, things that would be acceptable for character (going into that spooky basement, accepting that suicide mission, not asking for more supplies and support) are suddenly anathema. "My character would never do that" is the chant that comes out of the RPG side. Indeed, failure is frowned on, which makes it tough to write story.
Indeed, one thing that is commonly done for story is - you fail, but that failure is not your fault. That works, provided you don't go to the well all that often, as it still frustrates the player that his avatar is being foiled. Once your protagonist is also your participant, a new level of demands arrive. The covenant between designer and player changes. While demanding more versatility, the player also seeks to minimize their own sense of risk, even though sense of risk is one of the reasons to play the game in the first place.
The odd thing is, in order to get more dramatic options for character, we have to pry the chill fingers of participant off it. There are RPGs which start off saying "You are X" - an investigator, a government agent, a monster and go from there. But in doing so, you run the risk of reduced audience, and that is something that is very hard to to for the current structure of an MMO.
More later,