I've only watched the movies since my sister was a huge fan of the books, but didn't have anyone to go to the theaters with. I didn't mind it since it was actually a nice tradition that we did throughout the movie series.
I forget what film it was, but in one of them one of Harry's friends dies during a competition. The way he is so distraught over it seems like he is losing a friend he really adored, but they barely focused on that friend in the movies. Turns out this friend had a lot of parts in the books, but they omitted most of their scenes in the movie which really undersold his death and how upset Harry was over his death.