I like the art and the effects used (though I wish there were sounds or music too). I find it difficult to get used to aiming at the enemies correctly, but still find it cool that you managed to fit a whole leveling system within your scope.
By the way, for your future Godot games, use
get_tree().reload_current_scene()
to restart the game, triggered by a button or an input key or anything, that'll feel a lot nicer than refreshing the entire web page. I learned that from the "Your first 2D game" section in the official Godot docs.