Glad I played through the entire game. It's good to have 15 levels in the game with increasing amounts of zombies. I love the fact that there is a money system for me to either upgrade my weapon/army's weapons or build the army myself to kill those zombies.
I found this game too easy though and that's because I don't face any threat of failure. Another thing, my army don't get killed by the zombies either because I don't think I've seen zombies kill them. It's like they're letting it happen to them.