A good, solid game with some room for improvement
You say thsi is your first flash game? Wow, this is great. The Zombie Variety is amazing and you created something new the Defence genre.
My only complaints is that your its too easy once you find a good weapon, once you found all the weapons and have the maximum survivors you didnt have much to do in the day, and your teammates did nothing but shoot once per minute.
My suggestions is that
1) You make the weapons more balanced or uniqu. For example, the Uzi could have terrible accuracy but have tons of ammo and Vice Versa for the Snipers. Another Idea is to change the crosshairs for each weapon. (The snipe has a smaller retacle compaired to the shotgun)
2) Make allys more usefull (Shoot more often) or, you can give each survivor thier own stats and you can choose what weapon to give them based on thier stats
3)Add some more stuff to do during that day.
4) Add a "How long can you last" option
5) Add some strategy. Like search for food which decreases its numbers per day or items to make your baracade stronger.
Thats it! Sorry for such a long review and good work on this game! I look forward to you future submissions!