First off, before I get chastised for the heading, this book was very good, but it could have been amazing given the introduction of several new much better rounded characters and an all singing all dancing super new arena in the shape of a clock. As others have alluded to, it was to put it crudely, somewhat of a "rush job".
I won't give a pointless synopsis of the book like so many insist on doing as it is available above. However what I will say is that Suzanne Collins clearly hadn't envisaged turning it into a trilogy and spent about half the book going on and on about life in district 12 post the games, I have to be candid here and say I struggled at times to keep interested. Katniss doesn't really develop as a character nor do the first games seem to have taught her much, she is still the same brash, reactive girl. I gave 5 stars to the original, so I was expecting so much more from the sequel, unfortunately it was not meant to be. It was only when the announcement for the second games finally came about did things start to get interesting again, although by that time so much time had been wasted talking about Katniss's pointless wanderings since her last games that the conclusion was rather hurried.
I have read all three of the books, and therefore I can say with confidence that this in my opinion was the weakest although its saving grace is that I don't really think it's a sequel, more a gap filler between the first and third books. This second book could easily have been amalgamated with the third to make 800 pages, which would have made much more sense to me, rather than waiting another year between them.
Still definitely a prerequisite read to the third if you want to finish the trilogy but just a little flat given the tools at the author's disposal after such a brilliant first introduction to Katniss and Panem.