How do you compress a 30 hour game into a 2 hour movie? I wouldn't have high hopes for this. If it happens (and I doubt it will) it's going to be another dreadful adaptation like all other game-to-movie projects. I don't think a single good movie was ever made out of a video game. They've pretty much all sucked and Mass Effect will be the same, in spite of the quality of the ME series.
In fact, a TV series based in the ME universe (not necessarily about Shepard) would probably be a better idea than a standalone movie. It's about time we had a decent space-based TV series again and the ME universe would provide a lot of good material for an entertaining sci-fi series.