I've just been tweeted a link for a really interesting article from techradar.com which discusses why movies which are made based on computer games are never very well received.
I attach a link to the article here: http://www.techradar.com/news/computing/why-are-movies-based-on-games-so-terrible--602924
I think that it makes some great points, particularly the notion that those in Hollywood who 'greenlight' movies are not generally gamers (although I believe that this is set to change, given as almost everyone I know of age 18-60 has played a few games of the Wii, in the last couple of years), and that the plots to the films which have been made have been appalling. However I think that there are a couple of other poonts that the authors haven't covered. Here are a couple of my suggestions:
1. Act like a mainstream movie: Except for Tomb Raider1&2 (and to a lesser extent, the highly suspicious Super Mario Bros and Street Fighter movies), the majority of films of computer games have not featured any major stars. Now this could be because of the terrible plots, because of the bad reputation of computer game films or the pay (!) but it certainly isn't because there isn't an audience. Millions of people game, men and women, girls and boys alike, and all of these people like the cinema, but the game-film genre should be measured using the same rules at mainstream cinema. The films should feature at least 1 or 2 stars, a decent plot, maybe a big name director and a solid marketing plan. Imagine all the ways producers could market the product? Prominent viral marketing through the console itself (Xbox360 features are already big on this). Let's get a couple of sexy men in there too, people would flock to see a Brad Pitt GTA4 movie.
2. Heavy on plot, light on gore: All these typical gaming guys who are attending the cinema may like to bring their girlfriends with them. The girlfriends see the bloodlust that takes over their beloved the moment that the console light is switched on and are themselves immediately turned off. The fact is, even the most realistic computer game violence (i.e. Condemned, yuck) is not as vividly realistic as a film of someone carrying out the same shooting, stabbing, kicking, slashing behaviour. If the film can get a 15 rating rather than an 18, (and maybe a love interest, oh ok they can be of a Sin City origin if needs be) that will attract a much wider deomgraphic.
So in conclusion, ask Stephen King to write the script, David Fincher to direct, Robert Pattinson to star and Miramax to finance, and I am sure Fallout-Halo-Fable 5 will be a major success. Easy...