This video game would be a RTS,there would be at least 2 resources 1 being humans driven underground (city hatches are around the map) 2 metal scrap on the map. 1 works like usual game resources you get a fixed amount at the begining then upgrades can improve income or extracting from another location. 2 is a limited resource on the map that is used to build advanced units, you can take enemy scrap after you've killed a unit (with scrap.)
The Tech for the 3 races are below, with possible units, elite (super) units, and buildings
Square = HQ, homebase etc and buildings
Circles = Units including light, heavy, and flying vehicules
Hex = Elite or super units (except for human tech tree were hex's are truck mods)
The gameplay would be very mobile except for the HQ's mostly it would be pvp based.
Possible game senario: energy based aliens hungry for brains land while humanity is in the middle of a zombie apocolypse. Double brain feeding frenzy!
Might work well as a Starcraft 2 mod.
I'm tired, I'l hopefully add more tomorrow. Let me know if you have any questions!