It's not a throwaway, but it doesn't feel like THE NEXT INSTALMENT IN THE STORY. Batman doesn't appear. Superman is glimpsed on p1, talking to his daughter Lara about her little brother Jonathan. Its heroes are the next generation: Carrie (Batwoman), Lara (Superwoman-ish) and Jonathan (the Golden Child). They fight Darkseid, the Joker and Donald Trump.
That's about it, really. There isn't even a concrete ending.
The book's reputation looks more toxic than it deserves, mind you. Some of its goodreads reviews are seething with hatred. Mysteriously, none of them say they're pissed off because they're Trump supporters, but let's face it. The Joker has a Donald Trump glove puppet. (Literally.) Darkseid is being used as a Trump metaphor, so he wants to win an election (eh?) and he has a propaganda superpower that makes humans hear a message of universal obliteration and respond with "he's making sense". (This is underlined later when someone says almost the same words in response to Trump himself, ahem, Governor J.M. Bozo.)
"Perfect. Perfect. Law-abiding citizens will cower in their little homes, while my agents of chaos will flock to the polls." ...says Darkseid. Yes, that really is Darkseid.
That said, though, it's somehow even more topical today than it was on publication. "SAVAGE GOVERNMENT PROTESTERS BRING TERROR TO GOTHAM." The Joker's boys attack an anti-Trump rally and start a riot. (Their lethal force is trumped by Carrie, admittedly.) It's hard to read that without thinking of the 6 January 2021 chaos in Washington, incited by Trump because he said the 2020 presidential election had been stolen.
The other half of the story is public protests and riots. Batwoman can't fight Darkseid directly, but she can lead a mob. She throws things that aren't petrol bombs, but look awfully reminiscent of them.
That said, though, I don't think the book really works. It's interesting, but unbalanced. Like all Superman-Batman team-ups, it's struggling to handle the problem of the Kryptonians leaving the humans looking useless on the sidelines. Darkseid vs. Superman's children are what really matters. The Joker and Batwoman are little more than colour. Carrie's cleverer than Lara, admittedly, but the book's attempt at giving Batwoman the last word is interesting more for the message being shouted than for its awkward execution.
Carrie's cool, but charmless. She's in danger of turning into Psycho Batman from All Star Batman & Robin. (Surprisingly, Rafael Grampa draws her like a frill-necked lizard.) Lara's a sour-faced soldier who thinks humans are scum and at one point orders her brother to kill children. (It's very possible that he obeys, too.) Her hobbies are probably drinking vinegar and sucking lemons. Jonathan comes nearest to being worth reading, but only because his Buddha-like smug invulnerability is in contrast with him being a child. I found his cold fish expressions a bit off-putting. (However, he's sensible and well balanced, which is more than can be said of Carrie and Lara.)
Do you need to read this? Nope. The story's over. This is just a bit more in the same universe, because Miller wanted to write about the girls in the next generation. As an adventure, it's lop-sided. As a polemic, though, I found it quite interesting.