not bad, but there is room for improvement
this is a fun game. i personally like zombie games and deffence game and both of them together is awsome.
try making the crows more visible. i died cus something i couldnt see was attacking me.
ok my ideas: give inf ammo, make zombies faster and waaaay stronger, offer reload speed upgrades make crow easier to see, get hardcore zombie killing rock music.
make different modes-story(regular lvls), survival(zombies keep comeing non-stop and you can pause to upgrade)
an interesting mode would be Arena where you can chose what types of enemies go at you and the rate. when you beat story mode(maby 50 lvls) you can unlock a gatling gun to use in arena or survival.
Ok so thats all i can think of for now, pm me if you wanna brainstorm ideas with me or if u like what you hear. I play a lot of deffence games so i know what can be fun.
Hope you read the whole thing =D