Cato - I don't remember Cato being so talkative in the books. From talking sh*t to the other tributes to his little statement at the end about finally realizing he was never going to win, he was a talkative little fellow. And what was up with the relationship between Glimmer and him? What was she hoping? That by snuggling up to the big guy, he would spare her life? Kill himself so she'd win? I'm surprised he didn't just snap her neck while she slept. I also didn't expect to feel bad for him, but by the end, I did. His death was also slightly different. In the book, the mutts torture him for hours INSIDE the cornucopia before Katniss can shoot him, whereas in the movie he falls right outside the cornucopia and she is able to kill him quickly.
Katniss calling out for Peeta - One of my favorite scenes from the book is after the announcer says that two people may win if they are from the same district. Katniss automatically yells out "PEETA!" then covers her mouth, realizing she just gave away her location. I thought that this was when she first started to realize how she'd felt about Peeta all along. I was sad that all she did was whisper Peeta to herself.
Katniss poisoning Peeta - In the book, when the announcer says that there is going to be a feast and there will be something there that everyone needs, Peeta makes Katniss promise not to go. Haymitch then sends some sleeping medicine so that she can go and get the medicine from the feast. Peeta's feeling of betrayal I thought was an important part of their relationship.
Avox(es) - I don't know what the plural of avox is, but there weren't any. Yea they were there in the background, looking all weird. But we didn't learn what they were or how they became that way. I forget the name of the avox that Katniss knew, but she wasn't there. They skipped that part entirely. I guess it didn't really add anything to the plot, but I think it showed the savagery of the Capitol.
No Madge - They didn't show the Mayor of District 12 as having a child at all. Although I guess she could have been in the audience and not up on stage with her dad. In the book, she is the one who gives Katniss her pin, possibly knowing full well what it means. Instead it was just a pin that Katniss picked up at The Hob, gave to her sister, received from her sister, and then received again from Cinna. Again I guess it doesn't really drive the plot, but I think it would've been nice to see.
The Control Room - Since the book is completely from Katniss' point of view, we have no idea what is going on behind the scenes. We only know what Katniss suspects is going on. I personally, loved the addition of the control room. It was cool to see Seneca sweating, trying to figure out what was going to do. I loved how they showed it all futuristic and touch screen-y. I just thought it was an interesting juxtaposition of them in that sterile room making these life or death decisions while children are out there being the ones fighting to the death.
District 11's Reaction to Rue's Death - This might be mentioned in the book, but I think it isn't until book 2 or 3 that they mention this. Or possibly on the train ride home as they go through district 11. I honestly don't remember. Again, I loved this added scene. When District 11 gave the three finger salute, I lost it. I'm talking Severus Snape dying tears. (Those are the big tears.) The man who I am assuming to be Rue's father freaking out was beautifully done. Who wouldn't react that way after seeing their 12 year old daughter be viciously murdered? It just showed how absolutely human these people are and how they are having their humanity repressed. Loved it. Oh another thing, they never showed District 11 sending Katniss some much-needed bread. It might have been hard to explain, but they could've added notes like they did to Haymitch's gifts.
Is Katniss pretending? - In the books, Katniss is pretty much pretending to love Peeta for the sponsors, to keep the two of them alive. I don't think it was quite as obvious in the movie. I honestly don't know how I feel about this change. On the one hand, I love Peeta and Katniss together. But on the other hand, it doesn't set up the ending properly. The book ended with Peeta asking Katniss whether it was real or not and then he tells her to let him know when she figures it out. I really liked that ending and thought it set up her confusion and the next book much better. I'm interested to see where their relationship is at the beginning of the next movie.
Katniss Pulling Her Bow on Peeta - When the gamemakers decide that only one person can be victor after all, Katniss pulls her bow on Peeta and he tells her to kill him. In the movie, she doesn't pull the bow on him but he still tells her to kill him anyway. I think this was kind of important in the book because in the book she isn't yet in love with him and still has major trust issues. In the movie, it didn't seem like they were going for the same relationship. Instead they were focusing more on them falling in love so I guess it just wouldn't have fit in the story. I still missed it though.
The Mutts! - This is one of the things I was most sad about. In the book, the mutts (the dog like beasts) have the tributes face and possibly a touch of their personalities. Imagine Katniss trying to kill a beast with Rue's face. In the movie they were just monstrous and scary. Damn near gave me a heart attack when one of them jumped out of the darkness at Peeta.
Peeta's Family - I missed this one too. In the movie, Peeta mentions his mother once when he says that she thought that Katniss could win the games. In the book, his family is much more important. We learn that Peeta's father was supposed to marry Katniss' mother, that Peeta fell in love with her the second he saw her, that she used to sing her father's songs, etc. There's just a lot more family dynamic between the Mellarks and the Everdeens.
All in all, even with all these differences, the movie was still amazing. I loved the book and the movie and I can't wait to see the next one!