4. The Collectors
It's rare you'll glimpse the inner workings of any prototypical 'Mwahaha'-ing enemy races within sci-fi titles to see what makes them tick. Halo tried with the scene in part two where you meet the Flood-commanding Gravemind, and Gears of War occasionally gave a human face to the Locust in the form of Queen Myrrah, but so far there's never been a
villain whose motives were so fleshed out it makes you question your actions on the other side of the fence when all's said and done. At the close of ME2 it was revealed that the Reaper Harbinger was gaining control of the Collector General throughout the entire campaign, giving weight to the idea that The Collectors themselves were always acting against their will, or to some degree weren't as pre-disposed to slaughtering thousands as first thought. If there's one thing Mass Effect's world does better than all else it's letting you interact with far-away species' and understanding where they're coming from in a galaxy littered with opposing views and cultures. A revelation in Mass Effect 2 almost writes these guys out of having a say, as the Collectors are former Protheans the Reapers have repurposed and 'overwritten' to do their bidding, but diving into their headspace during this pivotal time in the galaxy's history would be fascinating regardless.