Another thing that should be added is when it's sunny out or daytime; the zombies stay in hiding. You could try to add that to another game mode setting, if you can get that to work....
I had an idea like this early in. However in practice the NPCs don't come out during the day. Zombies can only actively eat NPCs in the same area as the player, so it ended up with a rediculous scenario where by night the city swarms with zombies, then by day the zombies scurry away and the citizens go about their buisness like nothing happen. Hilarious, but completely misses the point

Anyway, update on what's left to do/has been done for next release:
Done- Player is now infectable/transforms
- Zombies consider zombified player an ally
- Player can command the zombies to follow him andlead his own horde
To Do:- Polish up options panel to reflect changes
- Add a mechanism for eatting corpses/hunger weakness
- Add a passive detection effect so player's unarmed attacks spread the infection to NPCs