Channel 4 has launched a new online game, called Routes. It's very ambitious and very pervasive. Not only was it broadcast on TV every night last week, but I was even able to interview one of the game characters. Matt Blacker, a "freelance journalist", filled me in on the exciting back story – scientist Markus Schoenberg has been murdered, and Matt and Markus's niece, Rachel, are trying to find out why. But not only that; Matt also answered questions about his background and even asked me if I knew of any freelance gigs going. The game is as deep as you want to push it to be.

Which got me thinking about what it is that we want from a game, and how it's different to what we want from a story. Superficially, games have a lot in common with other screen-based media: movies and TV shows. They have the same glossy production values, the same multiple franchises, the same all-action blockbusters. But games aren't movies; the interactivity that makes it possible for me to email a character in Routes and receive an in-game response pulls against traditional storytelling. I write both novels and games, and the crucial difference is this: in a novel I'm telling a story to the reader, but in a game I'm allowing the player to construct the story with me. There's a constant tension between allowing players to feel they can do what they want, and guiding them through a satisfying-feeling experience.

Adrian Hon, co-founder of games company Six to Start, wrote an interesting essay on the function of stories in games earlier this year. In it, he points out that even games which are praised for their narrative seem weak when placed alongside traditional narratives. He says: "if the story of Grand Theft Auto IV were a book, it would not be published and if it were a TV show, it would not be filmed. It is not a good story, and the dialogue is average at best."

I think this is true. And it's probably one of the reasons that games are criticised as being "lowbrow". But it doesn't make GTA IV a bad game. Valve's game Portal, for example, is a really charming, intelligent game; the story and the writing are top-notch. But I couldn't sell that story as the premise for a novel or a movie. "Computer goes crazy, warrior has to use cunning to take it down." I don't apologise for 'revealing the story' there. The point is that the story's not surprising. It was done well in 2001: A Space Odyssey and pretty much every sci-fi TV show since has taken a pop at it.

But for all this, Portal's story is fantastically involving. The reason is this: stories feel several orders of magnitude more intense when you're participating in them. Computer games are like dreams. Because they feel like they're really happening, they don't need to be complex to be involving. I've frequently woken up from a dream thinking "wow, that was the best story, I have to write it down!" only to discover that the story was "someone was trying to kidnap me, so I climbed a wall, found a gun and shot them"; it wouldn't even make a 5-second action sequence segment in a movie. But because I felt that I was actually there, it was far more powerful than simply watching James Bond shoot some villains.

Computer games work in this way too. The interactivity increases the intensity of the experience, increases your sense of empathy with the hero, increases your involvement in what can be a very simple narrative. So while I do believe that computer game narratives can be made even better, the characterisation more subtle, the stories less formulaic, it's not a criticism of them that this hasn't happened yet.