Maybe a check box to turn on/off advace zombie AI. As in, off would mean all the zombies would lock onto the closest player and try to attack them (like in Gamemode_Zombie). On would mean the zombies would only attack the player if they are attacked or the player is directly in front of them or if a zombie sees another zombie attacking a player.
Also, more standard zombies.
Zombie dumb: slow to everything, walking, responding to players, and other stuff.(like in the Dead Rising games.)
Zombie Smart: Fast to everything. (Like in L4d)
Then a zombie that is in-between Smart and dumb.
Better infection: If a player is attacked by normal zombies, nothing would happen. But if something like a hunter attacked them, they would have a sertant amount of time before they turn into a zombie. Then you could make items that would stop the player from turning into a zombie.