I've heard a lot of complaints in this area, and it seems to apply to just about every character, such as Katniss, Peeta, Gale, and Prim. I didn't love Mockingjay, but I didn't think character inconsistency was a problem. All of the characters have been through SO much trauma, psychological, physical, emotional, mental, anythingal. I think the changes brought to Katniss' character were interesting and helpful to the overall arc, rather than contradictory. She's realizing that a lot of her current personal problems are because of her upbringing in a crazy, crazy dystopian world, and at the same time she's kinda falling under the wave of all those issues. I felt a lot more empathy for her in this book than any of the others, probably BECAUSE she's starting to have some self-awareness. Peeta, okay, let's face it, Peeta has PLENTY of reason to have a bit of a 360 turn. I don't even understand the Peeta criticism. He gets tortured and completely brainwashed: YES, he's going to be a TAD unstable and different. :P Moving on to Gale, I think his character arc in Mockingjay was fully built up in the previous books. The only real fact we know about him in The Hunger Games is that he's said some treasonous things about the Capitol, and he's a survivor like Katniss. This goes further in Catching Fire when he's the firebrand in District 12 and, you know, gets beaten and almost killed, which only pisses him off more. Seeing him as an extremely bitter, genocidal vigilante in Mockingjay was not a surprise to me at all. And Prim. Oh, Prim. Somehow, you have enough of a personality in the first two books to completely contradict your personality in Mockingjay? Sorry, guys, I don't think so. We only see her as a young child; her developed personality is only there in a few tiny hints.
Collins clearly enjoys building up characters to be awesome, and then at their best moment or right after, they get killed, and get maybe two lines describing it, and then they're gone. Boggs? Finnick? Really? Prim only got a little bit more, and she was related. Er, to the MC.
I'm not sure if I'm complaining or not. I just thought the characters got the ax remarkably quickly, with little or no payoff for such a built-up trilogy.
I'm not going to lie, I thought the violence was over the top. I know what Collins was doing with it: she was shoving the brutality in our face to make a point about the fact that our world is going to end from vengeance and media and reality TV. But, tying in with the above paragraph on character deaths, I think she went a little far with it to the point of ruining anything enjoyable or jolly about the trilogy. I like authors to have points, but I don't like them to sacrifice their story to their point: literature can get away with this, popular YA doesn't. Also, even while the first two books were brutal and all, they still had moments of hope and comfort. The only kind bit we got here was the ending, which in my opinion wasn't kind at all: read below.
So after enormous causalities, extreme psychological trauma, and the knowledge that all of the characters have no reason to live, it's all okay because at least the Love Triangle question is answered and, you know, they live happily ever after and have kids.
By the time I got to the epilogue, I honestly couldn't care less if Katniss got with either guy, or about anything that happened in the epilogue. There was already so much brutality that a tacked-on sappilicious ending did not make it better, or up for it, and or make it satisfying. My satisfaction level was at 60%. Blarg. And I am (was?) a committed Team Peeta fan. I can't imagine how the Gale fans feel, when their guy just wanders off screen with a "and then he never wanted to talk her again" explanation.
So, those are my thoughts. I'd love to hear yours. :)