great concept making a 3D tower defence game!
Think it's a great job for a demo idea, few things to improve upon for moving forward.
I want to see an outline for the range of the towers i'm placing.
Make a greater delineation between the night and day. Send all the aliens home first, and THEN start the wave.
Great difficulty levels, might be an idea to have more chicken pens around the space to protect.
The weapon and alien attacks weren't clear, but i got the idea.
I hope you keep this game going and develop it further. Great job!