What spoils films from video games is the different kind of interactivity. In films, you watch and listen and if everything is right, you come away with an understanding, or a different view, or an emotional reaction, or sometimes all three.

With games, of course, you are in direct control of the protagonist(s), to one degree or another. So fighting games like Mortal Kombat fall flat because each player has their own preference as to which of the fighters they play.

The more complex the story of a game becomes, the more filmable it is but the less likely the audience is to be satisfied with the film. Fairly straighforward characters like Lara Croft or Kratos have to be given sidekicks, motivations and character traits they don't need in the games and that puts some folk off. Come to a fully-blown customisable character faced with a spectrum of moral choices, each of which has different in-game consequences - characters such as the Grey Warden or Commander Shepard - and you're going to please nobody!