A basic summary of the story in this issue is that Mongul makes his first appearance and he tells Superman to obtain a crystal key for him or he'll kill three of his friends who he had captured. Superman is then forced to go all the way to a planet near New Mars - the home of the Martian Manhunter - to find the key. As he gets there, J'onn appears and tells him all about the key and how it will activate Warworld which can then wreak havoc throughout the universe. Despite this warning, Superman still goes for the key and he and J'onn fight, and Superman ends up winning with regret in his heart. Then as he gets the key, Mongul appears and tells him to give it or he will kill Lois, Jimmy, and Steve Lombard. But after having thought about everything, Superman realizes that his three friends are not worth the millions Mongul will kill if he reactiveates Warworld and so he regretfully declines to give him the key. Then J'onn saves them before Mongul can kill them but Mongul quickly overpowers him and Superman and takes the key and leaves. Then J'onn is mad at Superman for failing to protect the key and Superman swears that he will get the key back or die trying.
I just want to say that one thing that really bothered me through this issue was the way Superman was portrayed. He's written as having an arrogant personality because throughout the issue, he keeps saying "I'm Superman! I can do anything and if I can't do it, then nobody can!" and "I can handle it, after all, I'm Superman." I really hated that. Superman isn't the kind of person who goes around bragging about who he is and thinking he can handle anything. Even after J'onn explained to him about how the crystal key will allow Mongul to activate Warworld - a giant satellite with city-sized nuclear bombs and macro-laser cannons that can destroy planets - he told J'onn to step aside because he's Superman and he knows what he's doing and he can handle it. Then when he got the key and was coming out while thinking about everything, he's still thinking to himself that he's Superman and can handle anything that happens. And in the beginning, when Mongul demanded him to get the key, he told Mongul that he said himself that he's Superman and not some lackey. All throughout this issue, Superman is written as being very arrogant, which I felt was very out of character for him. You'd think that he would listen to J'onn's warning and he just goes off thinking "yeah yeah, I'm Superman I can handle it." However, other than that, I thought this issue was pretty good. Mongul made his debut in this issue and I really liked how he was introduced. When he demanded Superman to bring him the key, he showed that he had prepared in case he declined by showing that he kidnapped three of his friends and then when Superman got the key and encountered Mongul in person, Mongul told him that if he destroyed the circuits on his suit that create the cube that held his three friends prisoner, then it would just crush them instantly showing that he thinks of everything. I also liked the feelings of regret J'onn and Superman showed as they fought each other and the regret Superman showed as he defeated J'onn. The backstory of Warworld was also interesting. I also liked how Mongul knew that the Martian Manhunter would go there to defend the key because he made Superman go and fight his own friend to save the three friends who had been taken captive.
Overall this is how I'd sum up this issue:
The Bad: Superman was out of character and had a rather arrogant personality.
The Good: Mongul's character was introduced pretty well. Other than Superman's arrogance, the character he shows when he meets J'onn was good. Warworld's backstory was interesting. Overall story was pretty good.