I enjoyed playing the game over and over to beat my high score. I especially liked the music getting more tense as you go through the stages. My only criticism is that it did get to a point in which the game felt repetitive. You could add more upgrades like a faster charge, or more enemy types such as a slower and tankier enemy. I do understand if you didn't have the time add more to it, though.
Overall great game! Keep doing what you're doing!