I don't know how to accurately review this book except for: It broke my heart. And I still loved it. I don't really know what to say without spoiling anything. 
While we know a lot about the general plot already, since Haymitchs Hunger Games have been described in the original trilogy, this books still manages to change everything. I understand people who might say that everything fits together a little too neatly, but for me it was completely fine, because it doesn't break the logic of the story.

For example: yes, we meet A LOT of characters from the original trilogy, but it makes sense for all of them to be there: they're old enough, Effie had to become part of the district 12 team at some point. Plutarch and Beetee already being part of the rebellion makes sense as well as Wiress and Mags joining in, which is consistent with why they were on board during the second quarter quell.

There were only a few parts where I was like "okay, this is a liiittle much" (

like Burdock being Haymitch's best friend, it certainly adds significance to the relationship between Haymitch and Katniss, but it wasn't necessary in my opinion.

). It didn't bother me that much though.

There are certain interesting parallels between Haymitch's and Katniss' stories, which also make sense to me

since the rebellion waited for someone like Haymitch, whom they found in Katniss

. 

I am not thaaaat sure how much message this book adds to the Hunger Games, because I feel like propaganda has been part of the original trilogy as well, but it certainly adds to the story and expands the lore - I personally think this book strengthens the original story. Since I read this book pretty fast and didn't have time to think hardly and deeply about it, I might see even more in this story than I do so far. This book also definitely explains everything about Haymitch and it made me sob, I had to take little cry breaks for the last 40 pages or something. And Suzanne really has a thing for deeply emotional epilogues.