Nice game! I'm impressed by the amount of content you were able to make. I finished the game and had fun, but I suggest adding a radar as the regular levels were quite large and it was difficult to find all the targets.
While the vulcan is a bit OP, it's more fun than the other weapons because of its power >:) By comparison, the mortar felt a bit underpowered for its fire rate, but maybe it just needed a bit more juice to sell it.