I would like to see an ALIENS game like Natural Selection mod with ALIENS universe.
Take the ideas from Aliens vs. Predator 2 with aliens (loved sneaking up at humans and doing stuff ;)) and marines. Marines need to wipe out aliens, set nukes, escape, or whatever they need to do (e.g., some players exploring, other players set up traps and sentry guns, a commander player watching the whole mission, someone be Newt (scratch that)). Each map should have various missions. It helps with RANDOM maps if it is possible.
Aliens, facehuggers, etc. do whatever they need to do (e.g., facehuggers look for hugging some faces! Aliens hide, stalk, jump, climb, slash tail, spit, rip, make those cool HGieger environments, yadda, yadda!). Aliens have a queen (commander) who lay eggs (resources?), command, and others.