Nice game! I really like the pixel art style. The 8-bit music is really good, but it gets so repetitive after a while. You could use random music for each level or assign a special song to each one. The attack mechanics are simple, but they fit the game well.
I think if you want to keep the game at this scale, you should definitely add more songs. You could also add a short storyline.
But if you're planning to expand it, there's so much more you can do!
