Love Harry Potter! I think this book is the first time my kids were taught to question if someone is bad, whether they are always bad, and vice versa. I do love that in the whole Harry Potter series...there are core good guys, but even within that core, there are lessons on who to trust and when. There has always been the struggle with Snape not being a nice teacher or a nice person, but still being trusted by Dumbledore that he is a good guy. But this time, bad guys are good, but they are still labeled as bad by authorities, and pet rats are really bad. It is one of the first Harry Potter stories that makes you frustrated in the end.
I forgot how often Harry, Ron, and/or Hermionie fight or stop talking to each other. In the end, we always think of them as the three best friends, but there are whole chapters and sections when they are bickering. I think it is good for these types of conflicts to be modeled in fiction because it is true. It is also true that the friends that are upset with you, but will still have your best interest at heart and worry about you if you are in trouble are the types of friends you fight to keep.