Thank you for the feedback! :D
I agree with the enemy's feedback 100%. I feel they even blend a bit into the floor. I am in the middle of redesigning the enemies art for V2 at the moment, and I will take that into consideration for the new design.
The upgrade menu definitely needs an improvement. I am adding in an animation for when it appears + disappears, so I am hoping that delay for the animation player to finish should fix that issue! Also I like your idea of mapping the selection to keys as well. I will play around with keyboard input rather than mouse for powerup selection!