Thank you for your detailed feedback.
Input mapping is a good suggestion. I've never tried implementing that in my games before, but I imagine it can't be too difficult.
Also, the P and R keys were used by me for testing purposes. The pause was for me to take screenshots easier and I forgot to disable that. Oops! Nice find, though.
Like other suggested, I should really include a tutorial to explain things better. The way to reach the secret areas is by finding hidden triggers that spawn new doors. The first one is right above the door that leads to the second area. You have to bomb the vertical green blocks, but leave the one touching the ground intact. You should then be able to jump from that single block onto the horizontal green blocks and reach a hidden door on the wall. The second hidden door is in the second section and is at the top right of the area with orange blocks above the spikes.
The fact that you chose to ran past the shooting enemies made me realize that I need to give players more of a reason to engage with enemies. Maybe item drops or some kind of ranking system.
Thank you for your suggestions. They gave me improvements to consider for when I make my next revision.