Can't wait for a sequel!!
This game is great, just some suggestions on the sequel
more levels
increase difficulty
new weapons: flamethrower, grenade, heavy machine gun, bazooka etc
maybe limited ammo, so once you've found all the weapons you still need to send people to find supplies
skills/attributes for your main character and the survivors, e,g:
building skill, exploration skill, weapon skill, healing skill. you can assign people on different tasks and their skills improve as they carry out the task
devote time on building improve your base by constantly uprading your defence e.g. adding towers, strengthen wall, digging ditch.
people have stamina, people who are tired need to rest and can't work during the day or defend during the night
bigger zombies, boss monsters
anyway keep up the great work!