First of all, the aiming & firing system needs to be improved. The speed of the copter needs to be upgraded. the map size should also be a bit more wide then long. So I rated it a 2/5 Until it gets improved.
The boss has too much health....
The zombie's do way too much damage...
There should be secret items....(Like a different weapon) that's invisible.... Or in a crate... But what ever I favorited & 3/5 :D