While the concept is very simple, the implementation of the Theme works quite well.
The Towers are interessting and look amazing, despite the Rather simple look.
Sound design is nice too.
However, playing the easiest difficulty got a bit boring, a way to speed spawns up would be cool.The Highest difficulty is a lot more fun however.
What you could ve changed would be allowing the Player to move the Camera, at least tilt it to look straight down. In the desert map as an example, far up are the good tower spots, but trying to build behind large towers like the Boster becomes a bit inconvinient.
Obviuosly the game becomes a bit boring after a while, since you soon reach a deathbox through which no enemy can pass, but tbh i dont have too many ideas how to fix this. What i would ve tried is making towers even rarer (by decreasing the money gained on kill) so the players have to Move towers around and cant lean back.
Concluding: 7/10