I want to like this game, but the same strategy works on nearly every map. Slow them down, hit them with the big guns. Toss in a couple lasers for airplanes. Hellfire the final wave. Rinse and repeat.
Enemy variety comes in the form of airplanes or ground units. Ground units may look different, but the only real difference is how much health they have. All of the turrets are effective against all ground units, it's only a matter of concentrating the most damage into a small of a space as possible. Not all that hard since 6 of the 8 weapons hit multiple targets.
This is a very vanilla tower defense game. I won't say it's bad, but it's not that great either.