I won't reply to all the topics in your post because, let's face it, there were about a hundred and thirty-seven, but....
book to screen: I thought the movie portrayed Katniss just about totally opposite of the book. ha. I mean, the major elements were there... took her sister's place, won the games, etc. but in the book it seemed like there was a lot of focus on Katniss not showing emotion or weakness in order to appear strong and win sponsors. She doesn't cry at all in the book but she cries several times in the movie which I think affects the way the audience understands her character. Also in the movie we don't really see any of the internal turmoil about the boys which makes her seem shallow whereas in the book she is constantly battling herself between Gale's betrayal (if he is even hers to betray) and her survival by pairing with Peeta. I'm not sure how either of those parts of the character could have been displayed on the screen but I wish they had found a way.
morbid book: I was in a bad mood pretty much the whole 5 days I was reading this series (my husband was out of town). I told my husband when he recommended the series that I didn't think I would like it because it sounded dark but with all the hype and the movie, I figured I'd give it a go and once I'm in a book series... well you know, you've got to finish it. I think when I read a book I so enjoy getting sucked into the other world that I usually just let myself, but with Hunger Games I was constantly thinking about the psychological repercussions of those stupid games. Ha! Talk about taking work home with you (I'm a counselor). Having read the books, I don't think I would recommend them to myself.
book to reality: I think it hit me strongly not as much on the real-world national level injustice but rather on the real-world my-work level injustice. I kept thinking about the kids I work with- particularly the kids who come from homes filled with domestic violence and abuse and how they parallel the victors. Survivors of awful brutality that they had no choice in, scarred forever and unsure what to do in "regular society" after the games (abuse) is over. Sorry, no resolution to this particular point- just sharing how the book accidentally affected me.