The sequel is always the hardest part of a trilogy, I guess. Whereas the first book in a series is building an entire universe, introducing characters and creating suspense, the second book is mostly about developing themes and leading up to the final conclusion and ultimate finale that will occur in the third book. Sequels are hard because they are 'fillers'. They do not create suspense, they prolong it. 
 Which is perhaps why "Catching Fire" is my least favorite in the Hunger Games series. It is still good, it is still incredibly fast-paced and completely consuming - but it fades a bit in comparison to both "The Hunger Games" and "Mockingjay". 
 (view spoiler)[Personally, I never really liked the idea of the return to the arena, of Katniss and Peeta in yet another round of the Hunger Games. It is an extremely bold choice for any author to repeat their own pattern so deliberately, and while I think Collins avoids the worst repetitions, I have always skimmed through the pages of training and prepping for the arena, as I've already grasped the concept of that so clearly in the first book. (hide spoiler)] 
 "Catching Fire" introduces a beautiful variety of characters and I especially like Finnick as a new addition to the series. I adore the relationship between Katniss and Peeta, and they share some really touching moments that almost ripped my heart out. They cling to each other in their desperation, and I cling to them throughout the pages, as they're the only source of hope the book can offer its reader. (view spoiler)[ My only complaint in Collins' characterization is Katniss' sudden weakness in the arena. It feels out of character for her. It feels wrong. (hide spoiler)] 
 Overall, I think "Catching Fire" does a worthy job in leading the series forward to its finale. It has some minor flaws, little parts that I disagree with, a hint of repetition and a poor writing style (did you notice all the question marks?!), but the book is still impossible to put down or let go of. 
 Once you've read "The Hunger Games", you will experience an insatiable hunger, an extreme degree of reading fever that will haunt you until you've finished the trilogy. Your heart will race and your eyes will never tire. You will devour every word as fast as you possibly can.