Found a (bug/glitch/)mistake :)
In Chapter 3, right before the checkpoint before the part where your gun tells you the mutants look cute, there is something inside a wall, possibly an enemy, which causes you damage if you touch the wall, can't be seen but can be killed.
It cost me a life so I decided to investigate. It's nothing too big, but it might seem like a bug to some people
Otherwise, great work. It keeps amazing me how simple elements can be used to make a great game over and over again! Keep it up 9/10