This game really requires a gun to that little car. As controlling the car in circle (octagon) is hard. Gun might have range of some meter and could be upgraded.
very good graphics. and kind of soothing music. the enemy kill sound could be better.
And to make the gameplay a little fast (as in to change the enemy and level a little fast) tower should have destroyed the big enemy when first timer goes off, right now it only detects the enemy and you have to wait one more wave. I think this could make more engagement.
but I really like what you made. I will give it some more try to reach the end level.