Average Tower Defense

A simple tower defence my buddy and I created. I documented the experience on my youtube channel DanuInDev, so if you are here from there Thanks for coming by. It is not finished so give me ideas on what spice I can add to make it a better game. 

The game has one world so far, with 4 towers and 6 total upgrades for 3 of those towers. Everything is saved and loaded when quitting and loading the game again.