Painful game to play when you've played the first 2 games, however, try playing it drunk! You'll find yourself swearing and grunting at your customers. Fun stuff!
What you need to beat "harder":
1 Large farm right next to you & more farms close to you.
1-2 Apartments or Trailer parks right next to you.
1 Hospital next to you or close to you, you won't need it right away.
1 Lab next to you or close to you, you won't need it right away but you will need to research as soon as possible.
Get as many churches and bars as possible and keep happiness high with partys!
Now, at the first turn remove all defenses and attack key areas with all you've got! Builders, doctors etc. and don't worry about it, for some reason these units rarely die in the first couple of days. Expansion is the key. Keep expanding until you engulf the goverment building or other game ending buildings. Don't try to take the whole map, just get enough so that the hordes can't reach your game ending buildings in 10 turns even if they overrun you. DONE!
This game is incredibly stupid on higher difficulties. I start game after game until I have 1 large farm and other farm adjectant to that farm. 1 or 2 squares for living. Hospital and research center nearby. Survivors to recruit nearby. EVERYTHING IDEAL! Then I do perfect strategy and aquire squares for maximun population growth, manage defenses so that I'm always protected. DOES-NOT-WORK! The zombies doesn't attack, they just build up until you are using all your survivors for defense... and then the horde arrives! You need EXTREME luck in order to beat this game.