20 Essential Comic Issues You Must Read Before You Die
4. All Star Superman #6
All Star Superman is one the the essential Superman stories and #6 demonstrates just why it's so great.
The issue is a flashback to the death of Jonathan Kent and reveals that Superman fighting the time-eating Chronovore caused him to miss the three minutes it would have taken him to save Pa Kent from a heart attack.
It's a sobering issue that shows a young Clark dealing with the concept of death and the idea that, even with all his power, he still can't save everyone. However, he still holds on to the optimism and the drive to do better that makes him the world's greatest superhero.