Hi !
So I think the main issue with the game is the lack of feedback to help the player what's going on. There are screen shake and particles, which is nice, but it would have been more important adding feedback when of the shield breaks, to really understand something wrong just happened. I had to lose once to fully understand what was going on.
Other than that, I think ghosts should spawn with a random y position, otherwise you can just spam and kill them (maybe they do, but wayyyy too late and I died before). It takes too much time in my humble opinion for ghosts to come from the other side of the screen, and it makes it more interesting so you could make it happen a bit faster !
Congrats on making the game ! It doesn't miss much to be great so you should work on it a little bit more :D