I'd like to see some other random AI survivors on the streets, running from and fighting the zombies. Then it can be like, do we worry about our own skins or do we help them out? If we help them out, are they appreciative and give us some ammo or something, or do they attack us to take what we have? Stuff like that would just add to the game, IMO.

Also, there needs to be some random weather conditions, like rainstorms with thunder and lightning or thick fog, and the weather should affect the gameplay. Like, when it storms, we should be able to make more noise with less detection because the storm screws up the sound, or when the fog is heavy it should be harder for the zombies to see us yet also easier for us to miss that zombie just standing there off to the side.