I'm a Jr in High School and I made my first iPhone Game. Suggestions/Feedback

Link to the game on the App Store: http://is.gd/U1L6

Its called Castle Defense for those of you wishing to search for it. It has been a 4 month collaboration with 3 other team members (1 other coder, designer, and composer). The two goals of the project have been to make a fun game, which at the time hadn't been done before, and hopefully be able to pay for my college tuition. I've learned a lot already however I would appreciate it if HN had any suggestions or feedback on the game.

Thank you, Greg