I give most of this book three stars, but the ending gets only two. I wish Collins had stopped after the first book.
The remainder of this review is all spoilers. Big spoilers. Only click the link if you're serious about your willingness to be spoiled.
I have two large problems with the ending: (1) Prim's death and (2) Katniss's lack of punishment for killing President Coin.
I get that this book is not a happy, joy, joy book, but reading is supposed to be entertaining. Right? So why, oh why, would the author kill off Prim? Upon finishing this book, I decided to take a step back and evaluate how this death might contribute to the overall story. My first thought was that, perhaps we had now come a full circle from the day the Katniss volunteered for the games in Prim's place. But no, instead of a full circle, what this achieves is only to defeat the entire purpose of just about everything that Katniss has done in the book. That's just depressing. Then I considered that Prim's death was used as proof to Katniss that President Coin was a big meanie. But no, the deaths of those children would have worked just fine for the purpose without Prim having been included. Lastly, I considered that this is just a tragic story, in large part, and the author couldn't let us leave without one more closely-felt death. Okay, then I move to kill Katniss's mother, or maybe Gale. Why Prim?! Haven't enough little children died in this trilogy already? After the death of Rue in the first book, especially given how Rue so strongly represented Prim, Prim should have been off-limits.
My second major objection to the ending is that Katniss is never punished for, or even questioned for an explanation about, President Coin's murder. President Coin was the leader of the rebellion, and presumably, most people thought that she was a good (yet power-hungry) person who led efforts to free them from oppressive Capitol rule. Her death should have been met with vengeance and outrage. Instead, we are locked up with Katniss for weeks while her trial proceeds without her input and without any updates to the reader. And then, she is just released. What?! Did I miss something? Katniss hasn't even explained to anyone that President Coin killed Prim. Is it just okay that Coin was murdered after leading her people to freedom from oppression? I'm confused.
Some side notes about the ending: I was also annoyed that, after fighting her way through the Capitol at great loss of life, Katniss was conveniently rendered unconscious during what should have been the climax scene, arresting President Snow. But I was pleased that Katniss chose the right boy. That helped to mollify me a bit.