Here's some feedback on your game:
1. Theme
I really like the idea of having to defend a pianist, but maybe add some more story, like, the ghosts are his nightmares or his stage fright or something like that.
2. Gameplay
The combat system is amazing, and power ups are also cool, but i don't really get the whole slot thing. When you choose the first slot you have only one, when you choose the second you have two attacks???
3. Graphics
The graphic for the ghost looks amazing. The animation for the player is also good and even though it isn't that fluid, i kinda like that style. But i would go for a darker style, with the only light coming from the pianist and maybe from a little lamp you have.
4. Sound
The soundeffects really add a lot to the gameplay, just like the particles, really great! The music is also good, but either make the pianist play something more dramatic or really make like this darker setting and everything and make more calming music like this one.
I would like to see you expand this concept, if not, maybe i will even do something like that in the future, because i really want to see a game with that story and everything.
I hope my feedback helped you a bit, and if you have time, it would be really nice if you could check out our submission too. Thanks! :)