Loved the effort put into this! The sounds really gave it some heart.
Gameplay-wise I think it's a bit lacking. The character feels slow to move even when you have only 1 heart left and the enemies besides the last boss aren't very engaging. Maybe increasing the base speed of the player and adding more enemies at once to compensate for the player's increased speed would help a bit.
But yeah, great job on your entry, it seems like you really enjoyed making it and it shows! :)