As I mentioned regarding the Hunger Games, I tend to judge books I know to be successful more harshly. It's a fault.
Anyway, Catching Fire took a bit of time to get into and Katniss, well, she's still a bit slow (which is okay, because half the time she's just a vehicle for readerly experience).
The parts of the story I find most compelling remain the games themselves and the moment of interaction between human being and technologized nature they represent. That's where Collins is at her best, that's what makes this story so compelling and intriguing for me. The rest, well...I find the broader world of PanEm to be a bit too contrived and not well enough thought out for it to be fully believable. There's just too much that doesn't match, too many instances where technology just doesn't work the way I would expect. The world-building feels rushed, as if there isn't much detail beyond the tidbits given in the book, nothing beyond the window-dressing needed to convey a setting.
What I love about YA post-apocalypse narratives in particular is how detailed and fascinating the worlds they invent are and The Hunger Games trilogy just lacks that.