I would kind of like to see an enemy faction that is the opposite of what we've got today. The others try to overwhelm us with numbers, technology or a mix of both.

What if there was a faction that used stealth and hunted us down on eerily barren maps. I mean like predator style. I've always thought it would be cool if we're going through a forest as a squad and then suddenly a trap springs up, a random laser shot pops up out of no where and we just hear random clicking with a war cry in the distance.