Nice submission!
Really liked the graphical special effects, assume a lot of them are shaders. The music and sound worked nicely and fit with the feel of the game. The story and gameplay was nice, although a little too easy - never died, a difficulty setting would have been nice. As some others have mentioned the ending of the waves drags out a little with the scorpions and probably could have been shortened.
A boss fight would have been fun at the end, although understand time constraints...
Thanks for submitting - it was fun!