one of the worst featured games i have played. i liked the penguin game that is similar to this, but this game takes forever to make money and it seems rather random how to go further.
Air mines are literally the bomb. Coupled with with the damage buffer and the auto air ship to draw fire and you have the recipe to make win. I liked running dual mine turrets to make sure the sky was covered with mines. The disk gun is also a neat idea and very effective.
When playing Gladiator mode after defeating a mage gladiator be sure to keep moving in a single direction because although the mage is dead any bolts he threw up are still on the way while you fight the next gladiator.