It's an interesting take on the theme, and I did enjoy the mechanics. There's some things I would like to see improved: The enemies projectiles are way too fast and are way too punishing making the game impossible fairly quickly.
So I would definetly make them slower. Also the idea of shrinking and growing is great, but the growing mechanic feels more punishing then it's worth, I think at least you should give more health to players when growing large as it's too easy for enemies to hit you with projectiles, and it's never worth growing large vs shrinking (in my opinion)
Other than that I like how you just start head-on -> straight into action. Good job!