Video games as literature?

When we made a list of potential ways to express literature on the first day of class, I think we ought to have mentioned video games. I have experienced some exceptional storytelling through this medium. Recently, I have been playing two games that differ widely in their approach to unfolding the plot. The first game, BioShock, involves making a series of binary good/evil decisions, seemingly to determine the course of things for the character. It is later revealed that you are not actually in control, and you have been manipulated into taking a very linear progression through the game.

The second game, Mass Effect, features a lot of conversations involving dialogue trees -- a series of different responses and reactions for the character to give. Each dialogue option is ranked on a scale of positive, neutral or negative reactions, but a negative reaction is just that; it's not a "bad" choice. Any given answer can take the conversation in a different direction, and so making many of these small dialogue decisions over the course of a 40-plus hour game drastically affects the trajectory the story takes. A supporting character dies, but if your friend played it in a different style, it could be a different person in their experience with the game.