I enjoyed the first two books in the series, but this book rubbed me the wrong way. The theme is Katniss' failure to adapt and her permanent brokenness from the old regime, but the ultimate ending is unsatisfying.
I relish dark and ambiguous endings, and it took me a lot of thinking to figure out why this one bothers me so much. The conclusion I eventually came to is that this book feels so nihilistic. There's no moral to be drawn here, no viable solution to a problem. If I had to put it into a pithy one-liner, I'd sum up the theme as "Nothing you do can possibly matter in the face of systemic corruption." Though the book doesn't assert any further thesis, the natural next statement that leaps to mind is "It's not worth trying."
And that, ultimately, is what drives me crazy about this book. Most dark endings serve as a cautionary tale -- "Don't do X or you'll end up like our main character" or "Watch out for the people and groups you choose to associate with" or at least "You should fight against the particular systemic corruption that caused this massive unfairness." I was unprepared for the bleakness of this book.
The book is strong from a writing perspective, and that gives it a formalist vigor that may be satisfying to some readers. There's still a page-turning quality here. It just was too empty to satisfy yours truly.