I really like the visual style, you've used some good colours and the shadow is really cool - it works so well. The orange square explosions are also really cool, a great little effect.
I think you need to speed up the starting gameplay by about 2-3x, it takes a good 90 seconds for the gameplay to start being fun 😅 I also have no reason to stop shooting, so an autofire option would be a good addition (and accessibility consideration)
For the game feel, there's a good start there. But all of the bullets need to be 5x the size, it feels like I've got a peashooter and I'm doing absolutely no damage at all. I think you also need some sort of sprite flash to indicate that enemies are taking damage, and a bunch of "popcorn" enemies that die in one hit!
I think once you've juiced it to hell and back, this will be a really nice little game :)
FYI this doesn't work on firefox!