As far as movie adaptions, one thing I really missed with the later Potter movies is the relationship between Tonks and Lupin. They showed the two of them getting together, but that was about it. I really like those two and wish we could have seen the part of HBP when Bill was injured by the werewolf (mind's spacing on the name) but Fleur still wanted him and I think McGonagall points out to Lupin that Dumbledore would have been happy to know there was more love in the world, and Arthur Weasley points out that even young healthy men don't remain that way forever.YES!
Finally someone else articulates my thoughts about that plot thread for me! It also bothered me, when I rewatched the final two films recently, that the only mentions of them having a baby are right at the beginning of Pt. 1, where Tonks starts to say 'Remus and I -' but gets cut off by Mad-Eye, and then right at the end in the forest, where Harry apologises to Lupin for him having to leave his son. If you hadn't read the books and didn't know that they had a child, those two seemingly random lines might seriously leave you wondering what you'd missed.
I appreciate when adapting a book for a film there are some things you have to cut for the sake of brevity - after all, two lines of text could well end up being a ten minute sequence - but come on. Like in the third film, when NOBODY ever really fully explains how Lupin knew about the Marauder's Map or what it was. Plot holes and inconsistencies bother me A LOT in books and films.
And back to books:
I really dislike books that are written from the point of view of a character you just want to shake. I can't remember who it's by now, but I read 'What about me?' a little while ago and just... argh. It was written in alternating chapters from the POV of a mother and her teenage daughter (Frankie?) and I just wanted to shout at the girl 'STOP BEING A BRAT!' I know that teenagers often are very self-absorbed, but the way she'd been portrayed as completely thoughtless in regard to anyone but herself made me hate her a little bit by the end of the book. I didn't enjoy it at all, which is a shame, because I thought the premise was good and really had a fair bit of potential, but when one of your main characters is that unlikable it ruins the whole book for me.
In contrast, I recently started reading Alan Bradley's Flavia de Luce series, and they are very well done. The main character, Flavia, is (I think) eleven, and for never having been an eleven year old girl, Bradley writes as one very well! She's a child, so sometimes I wish I could say to her 'don't be such a brat' or 'don't be so rude to your father' - but she's written well enough, and has enough depth to her, that it doesn't detract from my enjoyment of the story, the way one-dimensional-whiny-Frankie did in 'What about me'.