(SPOILERS) (Side Note: Don't forget to enter my Comic Con giveaway, where you can choose from several prizes, including a Hunger Games t-shirt.)
Last week I talked about why Prim actually needed to die to in Mockingjay to cement the themes of the entire Hunger Games series. A lot of people were upset and downright angry about her death, thinking it was pointless to the story. But it isn't. You don't have to like the ending of Mockingjay--I mean it's not as if we were meant to feel good about everything that happened in these books--but you can still appreciate and respect it.
A second problem some people had with how the series ended was that Katniss voted in favor of another Hunger Games. A lot of audience members felt betrayed, and they should--if Katniss had actually meant it.