Oh, how many scenes fall into this category!  I feel like the best way to approach this would be to re-read every book and subsequently watch every movie and then rant and rave about everything missing in the films, but to be honest, I simply don’t have the time for that.  So these are just a couple things off the top of my head that I remember feeling disappointed at due to their absence in the movies (not necessarily plot holes, just scenes I missed).

Sorcerer’s Stone 

  •  Snape’s potion challenge through the trapdoor – I don’t know why they cut this out!  Maybe to make the audience think that Snape was the bad guy for an extra scene by not including his defense?  Still, this was a stupid move in my opinion because not only would it have been a cool scene, but it’s also important in later books that Snape was acting as a good guy on Dumbledore’s behalf to protect the stone.  Not to mention the fact that it was Hermione’s moment to shine in the Sorcerer’s Stone; Ron got to be a chess master, Harry battled Voldemort, and Hermione got to… create sunlight with her wand?  Tend to Ron’s wounds?  Kind of lame, WB.

Chamber of Secrets 

  •  Nearly Headless Nick’s Deathday Party!  How awesome would this have been?!  Hundreds of ghosts, rotting food, musical saws, the Headless Hunt?  Plus it actually provided a reasonable excuse for the trio to be wandering around the halls.

Prisoner of Azkaban

  •  Every scene explaining the Marauder’s Map ever.  Come on, WB.
  •  …for some reason I can’t think of any other particular scenes that I feel are missing from the third film right now.  I’m sure there are, however.

Goblet of Fire

  •  Winky the House Elf’s entire plot line!  Without her, our only introductions to the world of house elves are through Dobby (waaaay too over-eager and annoying in the films) and Kreacher (just creepy as fuck) – we never get to witness the depths of house elf devotion to their masters and how twisted their treatment by wizards is.  She also helped to explain the entire Barty Crouch, Jr. plotline at the end of the novel… kind of important.  Taking her out simplified the plot but also made it seem way more two-dimensional (which is sad considering how million-dimensional JK makes the books).
  • Along the same lines as Winky, SPEW – or should I say, S.P.E.W.?  This was essential to deepening Hermione’s character in the fourth book; her obsession with SPEW was the first time that I became simultaneously exasperated with and in admiration of her endlessly stubborn sense of right and wrong, even when it aggravated everyone around her and seemed unreasonable.
  • The maze!  What was that maze?!  Okay, in the book, the maze was the coolest thing ever, and I wanted to go through it like every day of my life.  A spell made the world turn upside down; the Blast-Ended Skrewts attacked; there was a Sphinx – instead, we saw Harry run through a windstorm in between some bushes?  I don’t know, it was weird and really disappointing, especially as the climax task after he’d already fought a dragon and rescued his friends from mermaids.
  • Ludo Bagman’s awesomeness throughout the entirety of the Quidditch World Cup and the Triwizard Tournament – god, he would have made an awesome character!
  • Speaking of the Quidditch World Cup, how about including the Quidditch World Cup?  Biggest tease (and most unwieldy jump cut) ever.

Order of the Phoenix

  • I had totally forgotten about this until I read it online somewhere: Harry’s talk with Nearly Headless Nick after Sirius’ death when he asks Nick how people become ghosts and Nick explains that Sirius would choose death over a “feeble imitation of life.”  The concept and intricacies of death are one of the essential points of the series, and this was a pretty important addition to the overall message, especially because it was the first time that Harry loses someone he loves (no, his parents don’t count, he was one year old) and he is forced to accept that even in the wizarding world, death can be final and irreversible.  Also, after understanding the concept of Horcruxes, Nick’s statement takes on additional significance: Voldemort chose a “feeble imitation of life” by splitting his soul in order to avoid death.  (Side note: could Voldemort return as a ghost?  Was this ever addressed in any way?  Ahhhh!)
  • Percy betraying his family – this deepens the complexities of the Weasleys by about a thousand-fold and allows the most Epic Family Reunion Ever to occur in Deathly Hallows.  Sigh.
  • Neville’s parents at St. Mungo’s.  Huge character development piece for Neville, absolutely huge.  Also, it makes Harry realize that there are worse things in some ways than having dead parents, i.e., seeing them driven to insanity; it’s always somewhat gratifying to see Harry realize that maybe he doesn’t have the worst-most-melodramatic-life-ever-while-everyone-else-dances-in-fields-of-butterflies.  Everyone has secrets, and it’s a big moment also because the trio recognizes that you can know someone for years and still barely know them at all in some of the most significant ways.
  • “Weasley is Our King” – I just really want to know what tune to sing this to.

Half-Blood Prince

  • The meeting between the Muggle Prime Minister and Fudge – I just absolutely loved, loved, loved that opening (far more than Harry’s awkward flirtation with a waitress, which never would have happened in the books).
  • The battle at Hogwarts, which was important because not only did it reveal how the DA actually stood up and fought when they were called upon to do so, but it also explained why Bill was totally scarred thanks to Greyback (which would have been a far better manner of accounting for his injuries than the uncomfortable info dump at the beginning of Deathly Hallows).
  • Apparition lessons – it’s important to understand why all of a sudden the characters can go popping all around Britain without any problem in the seventh movie.  Plus, it would have been fun to see the students totally failing at appearing in hoops in the Great Hall.
  • All of Voldemort’s other memories that Dumbledore had collected through the years.  These.  Are.  Essential.  To.  Understanding.  Voldemort.

Deathly Hallows

  • Yeah, I’ve already addressed my gripes about Part 1 and hopes for Part 2.  See previous posts.