very very good
defense and shooter combo
10/10
the only hard boss is the first boss... but the bosses after him you should have a maxed or close to maxed machine gun and just spray n pray.
level one buy two tiles of spikes...
level 3 upgrade both tiles
level 5 by the machinegun
after that your gonna have to improvise :) pick your favorite turret or turrets and thats all there is to it.