Like cowboys vs zombies? Maybe even some bad ass indians head-shotting zombies with arrows? I'd play that. Perhaps make it a 3 way faction game. Make the zombies a little intelligent. And have the cowbros and indians fight the zombie faction whilst fighting over land control.
You may be on to something. I'm really digging the idea. I like the 2 factions vs a zombie invasion. -- Those who hammer their guns into plows will plow for those who do not. ~ Thomas Jefferson