I think it's interesting how sometimes people can look at the same thing and come to completely different conclusions. It happens with art, when two people have different interpretations of what a piece, particularly an abstract one, mean. It can happen with film, as demonstrated in many ways, though the the example I'll go with is the ending of Inception, where some people took the last shot to mean it was a dream and others took it to mean it was real. What's interesting about this though, is that in this case, the ending is only what started the argument. People went back to different parts of the movie to provide evidence that they were correct in interpreting the ending.
Which brings me to The Hunger Games trilogy. I have read all the books, and enjoyed the series overall, though I have opinions regarding the third book. (Seriously, you're just going to change the entire format of the series in the last one? The other two books were practically the same in set-up and order, then it was all different in the last one!) The thing I find interesting is how strongly people have reacted to the epilogue bit at the end. I've seen people say that the epilogue was terrible for wrapping up a complex and dark series in such a happy friendly way, and others who said the ending fit the series perfectly in terms to tone, that it was not so much happy, as optimistic. What strikes me as interesting is that often these people are using the same quotes to prove their points.
If a quote can be used by both sides to prove a point is it to be considered bad. Or is the power of said quote then strengthened. I think it's interesting because the difference between this book and my earlier two examples is that we understand the events of the epilogue. It was not left up to interpretation what occurred, it was explained. Unlike art or movies with ambiguous endings the question isn't what does it mean, but does it fit the story?
By definition, one could argue that because the author put it there it fits the story. But is it really the author who defines a story, or the fans? Does the author have an obligation to his or her readers to write an ending that will make people happy? It's the last thing people read. It's not like there will be another book that they now won't buy because they were unhappy with the previous one.
Maybe the debate about Katniss's life if what makes the ending appropriate. She lived a life full of pain and suffering, but also one of love and joy. To give her life an ending that is completely full of flowers and happiness doesn't work because she will always be haunted by the past. At the same time, one of her best traits is her ability to keep moving forward after adversity. Maybe the most fitting ending is one that isn't quite happy, and isn't quite awful, but is enough of both that people can argue it both ways. No matter what, Katniss will never have the life she expected, so maybe it's good that no one really got the ending they expected either.