Where do I start... The writers! I love Grant Morrison as a write and I don't know too much about the others but a solid 10/10 here. I Believe no other Superman story shows how and why he is the ideal hero as much as this story. It starts off with Superman doing what he usually does, saving lives by any means necessary. He saves an astronaut crew from certain doom on the surface of the sun. Of course this was a trap by Luthor who wanted to see the Man Of Steel perish. In any other comic Clark would've just kept on trucking but he notices that he is way stronger than before. He goes to get tested and it turns out his cells are dying and making him have new superpowers. Clark also gets terrible news he will die soon as well. Which begs the question what would any other person do in a situation like this, spend time with loved ones? Maybe do a bucket list of sorts. Rather than that Clark does nothing but selfless acts of kindness. In fact Clark acts like nothing has really changed. For Lois's Birthday he gives her a tonic that grants her Kryptonian abilities for 24 hours.
Rather than doing the selfish things anyone else would do he stays the same and helps everyone around him. Clark stops a person from taking their life, which is my favorite Superman moment hands done.
This comic just proves what I already know, Superman is the greatest hero, of all time
Disclaimer: This is just my opinion I do not regard this as fact or logic its all based on what you think/believe