Cool idea!
The only problem I can see is that I didn't feel challenged. I just place the strongest turret all the time and it felt like I was only waiting for the next wave to arrive. I never really felt treatened. Maybe making the game a little more balance to add challenge would be a good idea.
Other than that, menus are nice, the visual are nice (tho a little dark) and the Wilhelm screams are funny.
Keep it up!