I've been very interested in games as a new narrative form for some years. It is particularly exciting to be watching that form emerge. It's a time of great experimentation - game makers are literally inventing the form, discovering what is possible, and trying to discern exactly what story means in this medium.
But just as a film can't be judged by the standards of a novel - filmic storytelling happens in images, not words, as it must in a book - neither can game storytelling be judged by filmic standards. The very best games embed the story in the action (gameplay) relying as little as possible on filmic scenes to push the narrative forward. Portal is the game equivalent of a perfect short story, with the entire story told through action and environment.
Having said that, I also loved Bioshock (which does rely on cut scenes to move the narrative forward) for its rich, layered environmental storytelling, and its sheer narrative ambition. It's a grand, beautiful, flawed attempt at a game in which the story is of equal importance to the gameplay itself, and I think it mostly succeeds. I have not yet seen Grand Theft Auto IV, but I keep hearing that - despite its well-deserved reputation for violence and debauchery - it provides a deeper storytelling experience than any game that has come before.