Ok I played it again with WASD to center the screen and I beat all the waves. The game is much better balanced when you can see the whole screen and place towers strategically. Very nicely done.
One additional thing I would recommend is making it clearer where towers can be placed. It seemed random and unclear what was a good spot. There was even one place where I could put it in a boulder.
I updated my rankings for you based on this improved play experience.