Games are so much like movies now, it's not really worth making a movie about games anymore:
Discuss.
It just doesn't really work. Viewing a story through a video game is too different from a movie simply because of how it is told. In a movie you sit down and it takes you through the story over the corse of between 1.5-3 hours normally. In a game the story is presented over the corse of 20-60 hours, sometimes more and it is not simply given to you unless you are on a easy mode. You don't simply watch the characters because you are the characters. After every scene there is a space of gameplay, and between major moments normally a boss fight, which results in you spending time reflecting on what just happened and thinking about what is to come. Movies simply can't mimic this form of building suspense because they do not have enough time.
There is also a sense of achevment that comes from the story in games because you had to put some form of effort into getting from start to finish where as a movie the most you can get is "Woohoo I watched LotR extended version with out getting up to take a leak!!". I still remember when I finished CoP ToaU and ZM, these were done over the corse of a couple years and by the end the journy was as much a part of the story as the cut sceens. Stumbling up that damned mountain, finishing the last ToAU fight within 24 hours of it comming out, the crazy disfuntionally akward party set up used for ZM, winning DM with only 1 of us left alive. These are little tidbits that add a dimension that can not be mimiced on screen...
Or maybe I'm just cazy and the only one that thinks these ways XD