I am a fan of Tremulous, the open-source Q3 strategy FPS, to the point of writing fanfiction. Granted, it has no story.

    New Douglas was a peaceful planet, until the aliens came. Humanity used to live in luxurious cities, but now everything with less than eight legs lives in military bases. The aliens hunt the humans relentlessly, with the tiny Dretch or the magnificent Tyrant, or anything in-between.

    The light is burning my eyes... I have dust in nose... there's droning in my ears... it must be time to get up. I hate it here. I wish it were like the old days, with the farms, the trees, back when I was a child. I can't do anything about it but get up, pick up a gun, and pop some Dretches.

    "Hey, Alex, get up! You're on patrol at the greenhouse again. Boring as normal, I assume, but someone has to do it. On the bright side, this way you probably won't die today."

    Kirk was Alex's best friend, but he was a little hard on him at times. Alex was, however, more concerned with working than with joking with his friends. Greenhouse duty involved keeping Dretches and other aliens out of the greenhouse while the farmers worked. On the bright side, he got to use a jetpack. He would have to get a lasgun from the armory if he wanted a decent weapon, but it would be an easy day, so he just took his standard-issue rifle.

    Alex made it to the greenhouse without any problems. The greenhouse was the weakest part of the human's base, and it was on the exterior, but there was no reason the aliens would attack. The walls were strong and only dretches could get in through the vents. Dretches were easy kills for the machinegun turrets, the guards were just to make sure nothing went wrong. Worst come to worst, he could rebuild any destroyed turrets.

    Sorry for not putting more, but my fingers are sore.