I like LAN games a lot, but I find that a lot of them get old. It’s just the same thing over and over. What I’ve seen lots is where gamers take an existing game and make up their own rules. We’ve had ‘knife fights’ where people are only allowed to use knifes, grenade tennis, sniper war and plenty of other wacky game types. I think it would be cool to have a game that facilitates this kind of freeform gameplay.
I’ve always liked the idea of a facehugger battle. Two teams, humans with crowbars and facehuggers. Instant death.
Another idea is gauntlet, where one team just have to get through a narrow area without dying. They might get a jeep, the other team get mines and obstacles.
Zombie survivor. The humans have to band together against waves and waves of zombies.
These are all quite fun ideas, but it would be cooler if a game had a scripting interface where it was easy to setup these situations.