I would prefer it if aliens weren't playable.
I can only look with bafflement at those who think it is a good idea. And even more so to those who think humans are "boring". Obviously those people and I have completely different ideas of what constitutes "boring" in a science fiction setting.
Since I am one of those People who consider humans boring, I'll try to elaborate a bit.
In a game like ME we're presented with a variety of different species, one of them always being human and that one species usually taking the spotlight. Apparently some people can identify with humans easier, always create characters that are similiar to themselves, etc., whatever floats your boat.
When I look at the species in the game I don't favor humans over any of the others. I don't go "Hey, humans, that's my team! Wooo!" Instead I look at all of them rather indifferently and try to get a feel for them, learn about their background, decide which ones I'm most interested in and which ones I don't like. Humans have a disadvantage here because they're usually the same old species that they are in every other movie or game. I know humans, I've played them a million times and if a game doesn't do anything interesting with them, I'm not too keen on them by default.
In Mass Effect they soon started to annoy me. I wasn't indifferent, I was pissed at how much the writers favored this one boring race over all the others. Humans are already taking the spotlight of the game because of Shepard being the Protagonist, a member of the alliance and space Jesus, but it's not just the protagonist it's the entire species that started to give me Mary Sue vibes. They were introduced to the galactic society only 26 years or so before ME1. Other species waited for hundreds of years for a seat in the council, had loads of time to develop their technology, military, economy etc., but of course it's the humans that save the day at the end of ME1 and immediately get a seat or even control over the whole council without any of the other species giving them a fight. Of course humans also have superior genes to everyone else, so the reapers focus on them, of course humans have to defend earth at cost of all other homeworlds, while no one gives a **** about Khar'shan. I could go on, but you get the point.
I don't prefer humans over any other species simply because I am human myself. They barely bring anything new and interesting to the game, are often annoying and focussed on way too much and on top of that I always have to play them, eventhough the Alien races are much more interesting to explore. I'm not interested in Science Fiction or Fantasy Scenarios because of the hundredth portrayal of humans in a fairly stereotypical often heavily american influenced way, I'm interested because of their alien, supernatural and fantastic elements. That's why I'd like to be able to play as an Alien, I want to be able to roleplay as a member of one of the species that I actually like and that isn't bound to the same old human background as Shepard.