Mass Effect has immense potential for a movie.
But it'll never work out well--hollywood simply will never, under any circumstances, take a video game seriously.
Give me 10 years, and I'll do it right.
Having that said, I've never played Mass Effect.
Mass Effect is the best game I ever played. I'am looking forward for a movie, because this game is so good, that it's imposible to ruin it with "bad" movie.