Maybe I'm making a mistake by reviewing the book almost straight after finishing it because my thoughts are still so jumbled, but I want to express what I feel and think now and then if I don't agree with it later I can always rewrite this. 
 Firstly, on writing. The high-paced speed is well-preserved in the final book. Often one sees popular slogans like "It's such a page-turner!" written by editors, reviewers and other popular writers on book covers, but until now I've almost forgotten what a page-turner really is. Thanks to S. Collins I remembered what is it that I've always been looking for in a book, what kind of book is impossible to put down and what kind of book I'd like to someday be able to write myself. 
 So, when reading I've been thinking what is it that makes this story such a hit? How did Collins achieve something that every author aspirates to do? These are the aspects that come to mind first: 
 1. The plot is unquestionably original and unique. I was a bit baffled after reading the first book when people started mentioning King's The Running Man, some other stories about people being forced to fight to death written by Russian novelists, but now that I'm done with the series, it's obvious that even if Collins wasn't the first person to tell about a violent TV show in her book, it doesn't matter. The Games in the series are no doubt an important aspect and an irreplaceable symbol of atrocity, but the purpose of the story isn't solely to tell us that killing for fun is cruel. The Games in Collins' books are simply one of the means of completing the image of the dystopian world she created and describing the characters in certain unimaginably nefarious circumstances. 
 2. Now the characters. Collins' portrayal of all her characters is just perfect. Without tiresome descriptions and boring background history she manages to create a very vivid image of each character by putting them in certain dubious situations and showing us how people react. It feels like real life - actions speak louder than words. The only character who we can see from the inside is Katniss simply because it's a first person narrative, but although the reader is aware of all her thoughts and feelings, one still can't predict what will be her reaction to this or that event. 
 3. What makes the story sad? Grave spoilers ahead. 
 (view spoiler)[The series begin with Katniss trying to save her sister's life at all costs. She volunteers as tribute instead of her sister, Primrose. Prim is portrayed as something (well, someone) worth fighting and dying for, as a hope for a better life and in Mockingjay this portrayal is highlighted when Katniss finds out Prim is being trained as a doctor. Katniss believes that Prim has all the best qualities she could take from her parents and Katniss. Moreover, she says: "There's something else there as well, something entirely her own. An ability to look into the confusing mess of life and see things for what they are." And then Collins goes on and kills off this character, the only beacon of hope and reason for life. So can this not be sad? It isn't just another death of a nice and good character. It is symbolic. And although Snow and Coin were conquered, there are no feelings of utter joy because the central and probably the only thing Katniss was fighting for is gone even before the sturdy victory. 
 I was surprised, relieved and thankful that Katniss ended up with Peeta. Most authors have tedious and predictable love triangles (e.g. Twilight), which are repulsive to read about because the main character always ends up with someone flatly boring, with a moral side of a prince and explosive behaviour of a macho. Moreover, this guy usually is the girl's first love at first sight. Collins finally creates a realistic couple where people need deep understanding of each other and common life experience to be together, where a girl doesn't choose a hot guy just because he's hot, strong and fights for her. So thanks to the author for creating one of the most adequate romance story lines I've read about in years. 
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 Needless to say that the country of Panem was brilliantly thought-through, as well as the idea of 12 districts barely surviving to provide anything and everything for the country's government, the Capitol. The most picturesque episode describing the tragedy of it all was the reception in the Capitol when there was so much food and such a variety of meals that the wealthy citizens of the Capitol made themselves sick just to empty the space in their stomachs for more food while most of the districts were starving. 
 The Hunger Games series and particularly Mockingjay left me with an enduring bitter aftertaste of sadness, hopelessness, delight and reverie. I will definitely go back to these books later in life, and I do not understand people who were not moved by this story.