The art, story, background music and overall game mechanics are all quite good. Nice job!
However, I felt the shooting felt a bit wonky. Also, spamming the boss didn't really do anything except pull up my Windows sticky key dialogue. It would be better to use another key for shooting like 'Spacebar' or any of the alphabet keys.
Is there a way to upload the game directly? The idea of having to go through an installer may prevent people from trying your game.