Yeah, I guess so. The only really unique thing about ME was when they went retro with ME1 (something they abandoned in 2, curiously enough) and that's the one thing they probably can't translate to film without turning it into a big gag/parody (and we got that with Galaxy Quest, the best Trek movie ever).
I'm not sure what you mean by retro, but maybe it's just the fact that I'm not seeing it. I felt the aliens were like aliens in B5. Anyway, fact is, ME has a more developed plot and universe than most games, so it should be easier to make something that already has story to begin with. My only concern about a prequel is that we wouldn't get the Normandy on screen. It would have to more or less deal with how Shepard becomes a war hero. If they can tap the original script writers for the game, I could see this one being pretty good.