That would insta-kill you if they were in TF2's Backstab(Not Sidestab) range, and if they could crawl across walls and ceilings allowing them to wait for the perfect moment to drop down 3 stories, right onto your carefully coordinated squad, leap across the map, had destavating melle attacks, and could take out light scorces, making them and thier black skin(skin?) nearly invisible. Now imagine that instead of just going to third person and waiting for your teamates to help you, your controls lock, the game kills your mic, and you get to see a 7 inch long bladed tail stab your stomach, and then pulling itself out by cutting itself out horizontally. You're uncerimoniously dropped on the ground, and it skitters on all fours torwards your teamates.
Now imagine if the other half were spitters. The spitter could turn invisible, had a shoulder mounted insta-kill laser (That TOTALLY isin't overpowered at all), could set up futuristic insta-kill proximity mines(Spam. That's what's for dinner.), could jump like a hunter, and had a similar stealth kill to what I mentioned above, except with somthing along the lines of tearing off the victim's head, as well as a good chunk of the spine, and proudly pocketing the trophy.
And now imagine that the survivors are Marines with Assault Rifles, Flares, a Pathetic Melee, and an unaccurate motion sensor, that wouldn't do jack if it's moving carefully.
Now take all of it and pit the three against each other in the most terrifying Team Deathmatch you will ever play.
Then you have Aliens vs Predators.
Or, think of it this way. In a game of a 24/7 sudden death 3-way only 2Fort, with the Humans being the Soldiers (If they spot you, you're f*cked), the Aliens(The wall crawlers) are like the Spies (Intellegent use of stealth and sneaking is a must), and the Predators (Can turn invisible) are freakish, mutated DemoScouts.
