Cute tune and art work. The music was bit repetitive but I still liked the melody and instruments used.
I would suggest building on top of what you already composed.
For the gameplay I enjoyed the spawning of extra lill hench mushrooms. The switching to different mushrooms was a bit difficult and the enemies can go through walls where the bullets can't hit them I didn't complete the game and when I died the game just closed. A "game over" screen would be a nice touch.
With some tweaks here and there you have an even better game.