The wizard-filled world surrounding Harry Potter has become exponentially huge. Everywhere you look is a new Harry Potter-themed bar or a new line of merch. It does well to remember where all of this came from, though. A nearly unpublished book series written by one person.
The Harry Potter book series consists of seven volumes, each growing in size as they go on. There are hundreds upon hundreds of hours of content that the directors had to squeeze into understandable movie format, and so some things were removed and changed to make it all fit and make sense.
10 Harry’s Eyes
One of the first noticeable things that had a change is Harry's eye color. Distinctly mentioned in the books that he has 'his mothers' eyes' - bright green in color that makes so many people immediately realize who Harry is.
In the film, however, actor Daniel Radcliffe sported his own blue eyes. This is due to him finding contact lenses uncomfortable. He was, after all, a very young boy when the films were made! This carried on through the films and was not chosen to be fixed with CGI.
9 Peeves
Hogwarts is known for its smattering of personality-filled ghosts, like Saint Nick and Moaning Myrtle. Not all of them made it to the screen, however. Peeves, the pesky poltergeist, was cut from the script and never even properly tested on screen.
Some fans lament this decision, whereas others are thankful that the irritating mirage did not contaminate the otherwise lovely story. The character was going to be played by Rik Mayall - in fact, he was on set and was filming the ghost when the character got cut. The directors were probably scared of him overshadowing everyone else with a hilarious performance!
8 Charlie Weasley
Some would think that six children would be enough, but not Harry Potter fans. All of the Weasley family members were brought to the screen, except one: Charlie.
The second oldest Weasley child after Bill worked with dragons in Romania, which is a good excuse for him not to feature. He can technically be seen in a photo of the Weasleys on holiday in Egypt, and he is thought to be one of the dragon handlers that arrive at Hogwarts for the Triwizard Championship, but other than these brief glances his character is not around.
7 Blast Ended Skrewts (And Other Fauna)
To properly show off Hagrid's teaching ability and love for animals would take its' own movie, but fans wish that there would have been more of the school side in the films, especially involving his myriad of mystical creatures. Lockhart's annoying Cornish Pixies were one thing, but creatures like the Blast Ended Skrewts were sorely missed from the Harry Potter screen adaptation.
Even Nifflers weren't added until Fantastic Beasts!
6 Winky
In the Harry Potter books, the house-elves play quite a big part. Not just Dobby or Kreacher, either: Winky, Barty Crouch's faithful if not emotionally unstable elf, had a significant role in the books.
Freed unwillingly from serving the Crouch family, she worked at Hogwarts alongside the other elves. She falls into a depression due to her dismissal and begins to drink. This is probably why she was cut from the films, as it isn't very family-friendly to see a steaming elf on the screen.
5 The Gaunt Family
The seven books cover a lot of background information about most main characters, including Lord Voldemort and his past. Much of this was cut to make the films watchable length, and easier to follow. However, it is a little odd that the proper explanation of He Who Must Not Be Named's past was one of the changes.
The Gaunt family were descendants of Slytherin - making them pure blood and wealthy. After generations of inbreeding to protect the line, Merope Gaunt gave birth to Tom Marvolo Riddle. In the films, this is glazed over and only mentioned, not shown.
4 The Marauders
Possibly the worst commission from the books is the larger focus on the Marauders. There are a couple of flashback scenes, showing James and co. at school, and then Lily as a child, but that's it.
The books cover so much more. Notably, the film leaves out the fact that they created the titular Marauder's Map. Sure, the name is there, and watchers can put two and two together, but that is a pivotal item in the lore and some more information would have been greatly appreciated.
3 Breaking The Elder Wand
Some fans feel the last few scenes of Deathly Hallows part 2 were a little off. Mostly because it is different from the book in a lot of respects. One pivotal difference is the fact that Harry broke the Elder Wand.
This did not happen in the book: at the end, after the battle of Hogwarts, Harry uses the Elder Wand to fix his own wand and then buries it with Dumbledore. In the film, he stands on the bridge, snaps it, and throws it away. This change was probably done as it was easier to explain, but it comes across badly.
2 Dumbledore's Moods
"Did you put your name into the Goblet of Fire?" Dumbledore asked calmly. The keyword here is 'calm'. In the books, Dumbledore was easygoing and rarely got angry. In the films, however, he exploded at Harry when Michael Gambon delivered this line.
All in all, this is just funny instead of being a negative change. It makes more sense for Dumbledore to be worked up about the situation, and the darker mood of the films suits the anger. The only real issue is that it changed Dumbledore's personality from his cool sense in the books.
1 Harry’s Personality
One of the most noticeable changes between the Harry Potter books and their film adaptations is Harry's personality. The book Harry is a lot more brooding, a bit more sarcastic, and more of a 'teenage boy' than in the film.
This isn't necessarily a bad thing - the long, angry rants of Harry shouting in later books were omitted, which can only make the films better. But, the books show him maturing and learning to be nicer to others (such as Kreacher) over time, as well as cool his hot temper. It does, sadly, make him a little less interesting in the films.