I've gotta be honest.
This game really didn't have it all thought out. I mean ya, CoD:WaW is fun, but not in a flash game like this.
Pros:
*******
+ Upgrade System
+ Barricades just like in CoD
+ Difficulties
Cons:
*******
- Basically the same zombies repeatedly
- Environment seemed bland, maybe add a second floor?
- Not a huge variety in the upgrades
Overall:
*********
This had the potential to be a good game. It seems like you have a good talent for making games. However, the cons seemed to outweigh the pros in this one.