A high difficulty is a characteristic for arcade genre. I am sad that you couldn't appreciate fully the game because of your lack of proper controller.
However, you can still play it with keyboard (my friend Remoraki did a better score than me playing with keyboard, which is 34 to 10 when I am writing those lines).
The unintuitive of displayed keys is an issue already raised by a lot of comments, we are aware of this and if we had more time, we would have implemented this (now we have something to distinguish which controller is used).
Thank you for your comment, I hope that you will come back to our game when/if you have a proper controller in the future.