Mass Effect should not be a film. I can see no conceivable way that this rich universe of characters can be condensed into a two hour film. Rather, it can be done successfully as a TV series.
With a 13 episode arc, it would offer the creators more time to explore the different characters, feature more missions, all while following the main plot arc of the first game. Game of Thrones has proven it can be done, but what it also does is focus the writing on character development and drama, rather than loud bangs and spectacle.