A friend, engrossed in Film Studies at university, once explained to me the winning sequence in a trilogy.
The first is all about action. It gets the blood pumping and makes us care about the characters. Constantly seeing them in so much peril will do that.
The second has some action, but it's more about setting a scene. This is where we fill in the context and the background color. Our narrow vision pulls back and we see not just a world, but a universe.
The third is the grand finale, playing out the action on a much bigger stage.
She used the example of the Star Wars trilogy of films (this was back in the days before the three prequels). A New Hope was swash-buckling fun. Everyone loved it before it was the first. It was original, simple and made us love Luke, Leia, Han, Chewbacca and Obi-Wan Kenobi.
The Empire Strikes Back was the one which no-one seemed to like at first. But it's the one that everyone quoted and harked back to later. It took years for people to realize that it was the most important of the three. It had Yoda in it for a start.
Then Return of the Jedi painted its adventure over a much bigger platform, with plots and sub-plots, and a much bigger special effects budget. The older people whined about Ewoks, but mostly viewers thought it a stunning ending.
Suzanne Collins seems to have followed this same strategy with her The Hunger Games trilogy. I've not heard much love for Catching Fire, but I loved it. I hungered for more details - how this had happened, what led to these moments, what were the lives of the victors like throughout the past of the games.
In short, I wanted the history and I got it. One day, I think those criticizing this book will look at it like Star Wars fans view Empire. It's the deepest, most startling of the three.