Awesome
I think it's really great, congrats, but there are some details which can improve a lot the "addictiveness" of the game:
1st: If there's a rank when we game over, why not making a highscore board?
2nd: Maybe upgradeable stuff + powerups would be even cooler
3rd: I found some coloured enemies which didn't appear in the help menu, and they were hella strong and I dunno if they give me more exp or not :0
Anyway, really good job, keep it up