I think think the same. Zombies are more agressive and when you kill them, they respawn very (too) fast. When a single person is forced to kill a zombie in a town (without crossbow), he is lost. Every time when this happened to me, i run in a house and kill zombies till i go out of ammo and then are some zombies still left and i cannot escape => Killed 70 Zombies, i died and must respawn.