Cool idea. I really like the arcade feel to this game. As with other comments below I also enjoyed the 2D world more than the 3D one. However, it was still fun switching back and forth between them.
It took me a little bit to get used to switching between W and S to set the turret pitch in the 3D world and then A and D in the 3D world. This was minor though and once I got accustomed to I it was not a problem. Great submission!!!
FYI I also only played the downloadable version