Before I get destroyed, I'm not saying they should make a L4D3 so soon, I'm just saying when or if they do, I would love if it were set in the American Wild West. 
 
You know what is awesome? Saloon fights. You know what would make Salloon fights even better? Zombies! 
When you think about it, everything that the Wild West has to offer sounds even better with Zombies. 
 
Stage Coaches + Zombies  
Mine Carts + Zombies 
Dynamite + Zombies  
Trains + Zombies 
Horses + Zombies = ZOMBIE HORSES! 
 
ETC ETC. 
 
Prove me wrong!