Made quite some progress today. Tomorrow is back to work but I will add a front-end before I sleep.
1 - Swapped out the firing system with a Physics raycasting implementation.
This fixes the bug that Adam had highlighted earlier (turrets not shooting after wave 2 or 3).
2 - Added some sound effects downloaded from Freesound.org.
3 - Added particle effects when a tank is hit.
4 - Added a slowdown effect - each tank that gets Iced displays a blue square on the tank rear until the effect wears off.
5 - Restructured the game scene.
6- Added turret info when you hover over a turret button.
I hope I forgot none.
Add a menu and a You Die!! overlay and we have an official release here.
As usual the github project page has the latest update including the source code (Try not to add too much gold for yourself).
Here is an image of me getting owned by the AI :