Installing Java took me back! I like your palette choices a bunch, and the UI is very clean.
I did find gameplay a little lacking, though. You may want to consider shortening the amount of stages until you can use the special movement, the game is pretty repetitive until then. You could also consider adding a hold-to-charge mechanic to your shots, to increase damage dealt. It would offer a reason to not just spam the A button, as you could decide to take out stronger enemies with one well-aimed charge shot instead.
The game has great presentation, but I wish there was more depth. I look forward to seeing what you do next!