Weird and unrewarding.
Loosing wall health even though all attackers are dead.
This is defend the castle but 3D but done in a lazy way.
If this was your first game or just a milestone in your path, then congratulations! I wouldn't have released this until you fixed the problem with the armored guys walking off the map and eventually off the bottom of the screen and had a more rewarding gameplay loop.
Are the mobs just supposed to be standing around looking at you while you shoot them? I don't like this....