Oh god that's where I disagree. I enjoyed the serious and melodramatic aspects of Mass Effect and would rather a film focus on them and try to downplay the silliness.
I believe the series is epic and serious overall.
I dunno. For the most part, the impression I got from Mass Effect as a whole is a very comic book-ish space opera romp. What keeps me hooked on the trilogy is largely its sense of humor and lightheartedness in contrast to its serious undertones. Saren is so obviously sinister that it's hilarious. Benezia's lines are so cheesy that they hurt, but somehow a slightly good hurt? (masochism?) Sovereign's dialogue collapses under the weight of any serious scrutiny, but the vocal effect is cool. Salarians in general are hard to take seriously, which makes heartfelt moments with Mordin all the more meaningful. Seriously, salarians are one of those aliens that I can see being part of a fake alien-found-on-the-roadside video on YouTube.
Forget about Mass Effect 2. It basically takes this silliness to a head with its cast of misfits and ridiculous plotlines, with tragic backstories to add as much spice as their ridiculous outfits, except for Jacob I guess, who I guess plays the straight-guy in all this. Then there's the Illusive Man, who's so obviously a future villain that we just have to work with right now.
Even ME3, with its reaper genocide going on, somehow tries at times to stay generally lighthearted. I guess my thing is that these things help to gloss over what I feel to be an absolute mess of an overarching plot. While that overarching plot could (and should) very well change with a film adaptation, I don't think being all that serious and melodramatic throughout would do it any favors.
Really though, this is really the least of my concerns regarding any Mass Effect movie. I just don't want any kind of default Shepard, who chooses to do this and that, but I've come to terms with the idea that any Mass Effect movie is just not for someone like me.