The character development in this book was superb. We didn't learn much of Gale in the first book, but his real character came into light in the 2nd. By the end of the book we have a very good picture of who he is as a person - angry, passionate, willing to help others, and bottled up feelings for Katniss. The tragic history of Haymitch have also been touched on, but still left us with many mysteries into his life. Many wonderful new characters were introduced - Finnick (the best of all!), Annie, Johanna, Beetee, Plutarch, etc, many of whom will play a significant role in the 3rd book. Most of my favorite moments in the whole trilogy are in this book. The best one being the "sugar cube" encounter between Finnick and Katniss. The revelation of romance between Finnick and Annie in the Jabberjay trap was very touching.
The book gave us hints of the clever quirks past gamemakers put into the arenas, but nothing prepared us for what was waiting for Katniss and Peeta - "this is no place for the girl on fire." I love the reversed dynamics between Katniss and Peeta. Rather than survival, both already resigned their fates and were willing to sacrifice their own life for the other. It was a romantic tragedy between them. The carefree picnic by the beach with the other allies toward the end - and that kiss scene on the beach - was the perfect lull before the mind blowing storm awaiting them.
This book reveals the real cruelty of the Capitol and the manipulations of Snow that kept him in power. Tension progressively built up throughout the book, from the initial defiance in D11 and D8, the backdoor plotting between the rebelling districts, Cinna's open defiance with his mockingjay dress, until all hell broke loose in the end. I love the ending, with Katniss going berzerk over the loss of Peeta, and a wounded Gale revealing there is no more D12.
Overall a far and away better book than the first.