personally i think that it would be neat if they added more modes. such as
survival:classical--one this mode there are no special zombies, all zombies go slow, there are melee weapons, and much, much less ammo. the player even has to reload clips while others protect them.
instahorde mode--no special zombies, constand hordes.
minefield mode-- no boomers, tanks, hunters, or smokers. not many hordes. many, many withces that are silent.
army of two mode--only two charachters can play in this mode. however two players control one body psi-ops style, in which one person controlls movment and the other controlles looking and shooting.
personality mode--every charachter has their own perk. ex. zoey can reload faster, lous can run faster, bill can aim better, francis has more health.
pistoleroes mode--all charachters can only have revolvers, lomited ammo.
tank survival mode--just for fun