I think the theme saved you
Honestly it's not the best game out there. The idea is nice, however a zombie survival game is already out there, and it's damn good for a flash game (Last stand 1+2). The idea of a sandbox type game like this is pretty good, but to me it's way to slow paced and just not... fun. It gets old pretty quickly.
I also tried the Zombieman 2 and (odd that it's out already... eh?) that is better. That however seems a bit too hard and random.
Nah. People tend to get predetermined about something being awesome as soon as it involves zombies. This is not that good compared to what other games of the same style and genre have produced. The theme gives you 6/10 and the game itself is only 4/10. Therefore:
5/10 - You have a potentially awesome flash here. Still you need to work out some unique ideas and enhance the game mechanics if you want to succeed. I predict that the ratings will drop heavily soon.