Overall- Coming into this comic book, I was a little dubious, because I hadn't ever read anything by the writer of the comic, Peter J. Tomasi. With that being said, I was VERY pleasantly surprised!
This issue basically detailed the life and death of the Martian Manhunter. We are shown his death, in the detail that wasn't shown in Final Crisis #1. In FC #1, J'onn is offed in pretty much one panel, in a pretty quick, almost meaningless manner. It was like the villains killed him and just simply moved on.
In Requiem, we see that J'onn went out heroically, battling until he could no longer go on. Before he died though, he was able to contact some of his closest teammates and friends, Superman, Batman, Gypsy, Hal Jordan and Black Canary, and leave a piece of the history of the Martian race buried in the recesses of their minds.
While they slept, after J'onn had perished, these five heroes went about writing down the history of the Martians, as well as the life story of J'onn himself. I thought it was a nice touch that J'onn had them chronicle his life while they slept, so he wouldn't disturb them.
Before reading this comic, I really didn't know WHO J'onn J'onzz was. I was familiar with the character, sure, but I didn't REALLY know him. After this story, not only did I feel I had a better understanding of just how heroic J'onn was, I felt badly that he was dead, because I wouldn't be able to read any new adventures with him in them.
I really liked this comic, and the closing pages with Batman and the cookie were very touching and thoughtful. I'd score this comic an 8 1/2 easily. It was a tad slow at times, but it really caused me to care about the Martian Manhunter, who I'd never given much thought to before.