Overall, this plays like a pretty solid tower defense game. I do have some suggestions though. Some of the menu options don't seem to disappear on their own when you click on something else (e.g. I click on one tower to upgrade and click on another tower to upgrade, but both the menus are still open). I followed the instructions and still could not figure out how to sell my towers. The concept of using gold, corn, and money is okay..but was it necessary? And finally, The graphics could use a huge face-lift. Everything is pretty grainy and the colors look washed out.
Good game overall! I look forward to seeing some improvements. :)