Let me say that although it isn't quite as poignant as Dark knights: Metal it is still a very entertaining read by Greg Capullo and Scott Snyder.
The issue starts with Uncle Rock speaking to the reader explaining how they were in the shit now.
We cut to the Supermen who are in the final crisis and trying to convince Darkseid to help defeat Perpetua with Darkseid denying.
We see Wondie imprisoned by Superboy Prime, he explains how as a child he felt lucky to live in a world where heroes walked the earth. And the promises he made to the BMWL to preserve that earth.
We cut to Gotham and see the three Flashes being chased by the Darkest Knight as they are trying to make it to the mobius chair.
We then cut to Swamp thing, Harley and Jarro they are met by the Robyn king who is holding Jonah hex's head and he proceeds to stab Jonah's with a knife forged by Neron the lord if hell, which sends him to the darkest pit Masak Mavdil where he'll be tortured by resembling people he's sinned against.
We cut back to Diana who convinces Superboy
That BMWL was manipulating him, and convinces him to shatter the crises.
Everyone manages to get back to Gotham ( I guess) with Wally being in the Mobius, only for everyone to be told by the Darkest knight that secretly rigged the chair tore direct all its power to him.