But, in response to the topic, no. They're not really any major bad guys that would interesting to play as. Their stories and backgrounds just aren't very interesting. Plus, the whole point of the Metroid series, IMO, is the distinct gameplay as Samus, using her various Beams and getting and utilizing upgrades and such. Playing as a "bad guy," such as Ridley, for example, would have none of that, and be quite boring, and lose the that "Metroid feel." The gameplay would also be completely different. Maybe in a different game series, such as Zelda, it could work, though. I mean, playing as Ganandorf would definitely be cool as hell, and the basic gameplay wouldn't be too much different from Link's.
does anyone else see metroid 5 happening on earth, with samus blowing away human after human? i know that's what i thought when i watched both the alien: resurrection and fusion endings for the first time ...
I myself could see Master Chief and Samus somehow being tricked into fighting each other by the Covenant and the...whatever group of enemies Samus would be on at the time. And if it must be on Earth, so be it.
How about a Metroid virtual pet simulator for the DS where you raise a Metroid from larva to Omega and train it to hunt and kill at your bidding? That's about the only halfway decient way to play as a Metroid baddie that I can think of.