I have to side with all the five-star reviewers!
I enjoyed reading this SO much! I thought that the characters, who we have learnt to love in the previous books, developed new layers to their personality - Peeta in particular! A lot of other reviews have suggested that Katniss is unlikable and that she becomes weak and 'whiney', but I found her one of the most relatable characters BECAUSE of her flaws. Her reactions to the trauma that she suffers makes this one of the most gut-wrenching books I've read.
I think that the source of a lot of disappointment for the other more negative reviews is that this story has a non-conventional ending. I think the ending may have alienated a lot of people as it's not a stereotypically 'happy ending' but, personally, I found this a fantastic thing! With other series of books I've read, notably Harry Potter, although I loved them, I found myself asking just how much of a happy ending there could be for the main characters when so many bad things have happened in their lives. I loved the bittersweet ending of Mockingjay, where we see a world still affected by the traumatic events of the past.
I think that in comparison to a lot of (dare I use the phrase) 'Young adult' fiction that shows a dull love triangle, this book shows that no matter what happens, there is always hope and I found this to be a refreshing message. This book won't be everyone's cup of tea but I would encourage everyone to read this book - but maybe ask them to forget about the conventional ending that they were probably expecting.
There are flaws in this book, don't get me wrong, but I would challenge anyone to find a perfect book. For me, I review a book depending on whether I felt anything for the characters and whether I would read it again. By those criteria, it deserves every one of those 5 stars.
I hope that this has been helpful in some way!