Very cool and ambitious game! I really liked the idea of protecting the castle and the upgrade system. I also enjoyed the large map and the fact you could just walk over to where the skeletons spawned. To make the game more interesting you should obviously add more enemy types and maybe even more upgrades. You could add a fire or lighting arrow or something like that. Instead of just stat buffs you could have made a skill tree, but obviously that would be too much for the timespan. Overall awesome job!