Aliens Versus Predator 2010.
Now, as the title would suggest, the game is really, really fun when you have xenomorphs fighting predators, but to ensure there's a large number of both, the best thing to do is to set it to Species Team Deathmatch. See, this means that there are three teams, Humans, xenomorphs and predators. Most of the time, the last two grow very populated, but the first doesn't really fill up all that much. This leads to cases where the match will start literally a second after a person joins and is assigned as a marine. That way, there's only one marine, and they're more than likely to leave, meaning worse comes to worse, there's still a lot of preds fighting xenos.
I've been in that situation lots of times, but once in particular I joined a 7v7v1 match. Seven predators, seven aliens, one marine, me.
Took em to the cleaners and had them wrung out. Ended the match 150 to roughly 60. Felt good.
Captcha: twenty eight days.
The infection begins. To the bunker!!