A lot of fan service (maybe too much). Basically every character from Catching Fire onwards who was already alive during the 50th Hunger Games makes an appearance - except maybe Tigris but she was featured in Ballad.
Overall, I feel like this book doesn't do Haymitch's character any justice. Now, it's even more offensive that he never tried to mentor the tributes in District 12 until Katniss called him out on his shit in the first Hunger Games book.
I also found that there were way too many quotes of Edgar Allan Poe's "The Raven" in this book. I got really angry in the end because it felt so cheap. The last two chapters basically consist of not much else...
Moreover, Haymitch's relationship with Lenore Dove (awful name btw) didn't feel genuine to me. I just couldn't buy their love story. Their relationship is already established in the beginning of the book which made it harder for me to root for them. I just didn't catch what drew them into each other.
[SPOILER AHEAD!!!!!!!
And what the hell was this with the graveside in the woods? Lucy Gray's tomb just randomly makes an appearance?! I guess, Suzanne Collins just wanted to bury the fan theory that Alma Coin is Lucy Gray...]