Outside of the interaction with more 'alien' aliens, I would like to see a larger focus on non-humanoid species as well. I appreciate when the writers of a setting can make the aliens feel foreign to us, but I like it even more when the aliens in question don't look like a human in a rubber costume. Obviously, animation for such things comes at a cost, but I personally think that such an expenditure of resources would be worth it to help distinguish a game like ME from 99.9999% of all the other mainstream sci-fi settings out there. Plus, as an RPG with multiplayer capabilities, its a crime to relegate non-humanoid aliens like the Rachni and Elcor as glorified background props (IMO).
Now granted, the multiplayer side of things isn't everyone's cup of tea, but it would provide the perfect testbed for such unique kit ideas, and robust animation skeletons. Keep the single player campaign filled with rubber fore headed human look-a-likes if you have to, but multiplayer doesn't really have an excuse to not add such outliers to the game.
*Mini Rant incoming*
I am still baffled as to how some people can go on and on about how such requests are too hard or impossible to do when we've had something like Gears of War 3's Beast Mode that came out years ago for a third person shooter.
It's obviously not because such non-humanoid kits are impossible to do. And it's obvious that adding in such elements didn't take everything else away from the rest of the game. I would like to see BioWare put forth the effort and give us something truly alien in appearance to play as in MP, at least show us that the entire universe isn't inhabited solely by creatures with just two arms and legs and one head.
*End of mini rant*