Accidental Aesop: Hermione's subplot could be interpreted as, "Doing well in school is great, but your mental health comes first. If school is putting a strain on your well-being, it's not worth it."
Alternative Character Interpretation: Sir Cadogan, the portrait that takes over guarding Gryffindor Tower for The Fat Lady after she's attacked by Sirius Black, and whose work style involves setting "ridiculously complicated" passwords, and changing them at least twice a day. Is he stark raving mad, or Properly Paranoid taken Up to Eleven?
Ending Fatigue: Not too bad, but off to see Buckbeak get executed - diverted to shrieking shack, long Plot Dump, Werewolf ensues, time turner, going back though the evening and THEN it's over.
At one point in Harry Potter and the Philosopher's Stone, Scabbers bit Goyle on the knuckle (which was even referenced by Fred and George Weasley in Azkaban). Come Azkaban, and the revelation that Scabbers was actually Peter Pettigrew, who was the true person responsible for leaking Lily and James Potter's location to Lord Voldemort and thus their deaths, not to mention the revelation in Goblet of Fire that Goyle's father was most likely one of Pettigrew's comrades among the Death Eaters it becomes somewhat disturbing.
Ron carrying him around in his pocket and Scabbers even falling asleep on Harry's bed at one point in Philosopher's Stone.
Growing the Beard: Many fans believe that this is the turning point for the series as a whole, citing the encounter at the Shrieking Shack, the darker emotions and actual feelings of loss Harry feels about his family (that had not been really explored in the previous books) and of course the Bittersweet Ending. Sirius is proven innocent to Harry and Dumbledore but remains on the run alongside Buckbeak, and Lupin has to quit, while Harry worries about Trelawney's prophecy and the consequences of sparing Wormtail potentially bringing Voldemort back. Compared to the out-and-out positive victories in the first two books, it was bleaker and prepared for the gradual darkening of the remaining books.
Idiot Plot: The denouement at the end depends on the following characters (Snape, Remus) suddenly forgetting the following details:Remus is a werewolf, tonight is a full moon, and Remus has to take the Wolfsbane potion. Remus forgets about it entirely, despite the fact that he has lived with it all his life, which can only be explained in a character sense about how seeing Sirius and Peter Pettigrew on the Marauder's Map makes him think differently. Snape however comes to Remus room with the Potion (which he mentions during their confrontation) and despite having had a traumatic experience in his youth at the Shrieking Shack, still goes down there to meet Remus without having any real backup plan against a werewolf set to transform. Without this contrivance, Peter Pettigrew would not really be able to escape and Sirius still be on the run.
The part where Snape gets insulted by the Marauder's Map after Pottermore revealed that it was designed to do that to Snape and only Snape, not just anyone who tried to read it without the password.
In the novel, Hagrid expresses worry that Buckbeak might have encountered werewolf!Lupin in his escape from Hogwarts. As the movie illustrates, Hagrid need not have worried for Beaky's welfare in such a fight.
It Was His Sled: Sirius ain't evil. Lupin is a werewolf. Ron's pet rat Scabbers is really Peter Pettigrew, a human.
Hermione's white face.note The only line in the entire series indicating Hermione's skin color, used as a justification for fans that were surprised the casting of a black actress in Harry Potter and the Cursed Child, even though theater casting has always been color-blind like this; for example, there are adaptions that make Romeo and Juliet black too, even though they are supposed to be medieval Italians.
One-Scene Wonder: Aunt Marge only appears in one chapter (which has her name on it), but still manages to be among the more despicable characters in the series, perhaps even more so than her brother Vernon.
Shipping Goggles: The series has enough of this to fill a page, but this entry probably has the best example, what has been dubbed "The Symbolic Flight". This theory states that because Harry and Hermione flew together on Buckbeak together and without Ron, that they are destined to be together - ignoring the fact that Ron was only not present because he broke his leg earlier.
YMMV tropes present in the film:
Accidental Innuendo: The scene from the book listed above is even more dodgy in the film, when Harry's Uncle Vernon keeps bursting into the room to find out what's going on. Vernon is played by Richard Griffiths, AKA Uncle Monty.
Base-Breaking Character: The Shrunken Head on the Knight Bus. Some find him bizarrely out of place and unnecessary, others find him a nice bit of comic relief. It's worth noting that it was approved by JK Rowling - who prevented Alfonso Cuaron from inserting a choir of tiny people playing the piano.
Better Than Canon: The Adaptation Expansion for the Time Turner sequence is widely agreed to be a big improvement over how it was handled in the books. A few readers missed the Foreshadowing, and thus found the twist to come really out of nowhere. The film expands on this - having Hermione suddenly turning up out of nowhere in classes at points throughout the film. Also the twist that Harry himself conjures the big Patronus is Foreshadowed by having more events influenced by the time travellers - throwing the pumpkin seeds to warn that Fudge is on the way for example.
After everyone arrives at Hogwarts to start the new year, the Fat Lady won't let them into Gryffindor Tower because she's too busy trying to shatter a glass with her voice.
A lot of screentime is devoted to a blue bird flying through Hogwarts and twittering around; far longer than normal for a scene transition. The deleted scenes show that the sequence ran even longer - with the bird buzzing around Hagrid's head before getting shooed away.
The choir singing an arrangement of the witches' chant from Macbeth... along with croaking toads?
It should be noted that the first two here do serve some purpose in introducing the Fat Lady and the Whomping Willow tree (or just refreshing viewers' memories for those familiar with the series) so that they don't come out of nowhere when they become relevant to the plot. But the frog choir? Yeah that's just straight up Hogwarts BLAM.
Broken Base: Half the fanbase considers this one of the best (if not the best) Harry Potter film in the franchise, or at least when the Harry Potter films started getting good. The other half considers this movie to be one of the worst (if not the worst) Harry Potter film in the franchise. The film was mostly better received by critics than the first two, although it was the first HP film not to get four stars from Roger Ebert. Also, this is J.K. Rowling's favorite film. General consensus seems to be that the cinematography and visual effects are excellent, but the acting and script bring it down in places.
Continuity Lock-Out: This was the point when the movies started to get hard to understand for anyone who wasn't already familiar with the respective books. Most notably, this movie never makes it clear who Padfoot, Wormtail, Moony, and Prongs are, despite later movies operating on the assumption that the viewers all know.
Critical Dissonance: The film was adored by critics when it came out, opening to the most critical success any Potter film had seen at that point. On the other side, it left the Potter fanbase fairly polarized.
Darker and Edgier: Much more so than the previous two films, signalling the shift in tone for the remainder of the series.
Growing the Beard: According to most professional critics, along with about half of the fans. At the very least, people agreed that the younger actors and actresses were finally fitting snugly into their roles (aside from the Narm mentioned below). What's more is that this was the first film to make deviations from the book in the name of Pragmatic Adaptation, paving the way for the future films to do so (without falling into In-Name-Only).
Internet Backdraft: Best movie in the series? Worst movie in the series? Middlingest movie in the series? Whatever your opinion, a huge chunk of the fandom will loathe you for it.
The movie is full of it, most notably Harry's crying scene in Hogsmeade (blame Daniel Radcliffe), Draco getting attacked by Buckbeak (blame Tom Felton), and the punching scene (blame Emma Watson, Tom Felton, andSteve Kloves).
Apparently "believing in yourself" equates to SHOUTING AT THE TOP OF YOUR LUNGS. No quiet confidence in the film version of the Potterverse. EXPECTO LOUDYELLUM!
Malfoy being attacked by Buckbeak, which was deliberatelyNarm-y; in the book, it was stated that he over-played how bad the injury really was. Why? Because he's Draco Malfoy and he's a whiny brat. And because he wanted to get Hagrid fired.
Sirius's "I Know You're in There Somewhere" Fight with Lupin, wherein he makes a futile attempt to use The Power of Love and The Power of Ham to convince Lupin to not turn into a werewolf. And then Lupin does turn into a werewolf, which looks like a balding chupacabra (unlike the book, where werewolves only have slight physical differences from normal wolves).
The sheer number of times the whirring sound effect is used for any and every spell that is cast.
Narm Charm: The examples in the above entry, as well as "You foul, loathsome, evil little cockroach!" They're a near 50/50 mix of awesome and narm.
Never Live It Down: A lot of the fandom's complaints with Hermione stem from this film. Namely her getting Ron's line standing up to Sirius and her action scene on the Whomping Willow (despite the fact that she gets into a worse scrape than Harry in that one). If the fans ever complained about Steve Cloves turning Hermione into the Creator's Pet, expect this film to be mentioned as the root of it.
Alfonso's complete redesigning of Hogwarts geography, coupled with the overall more comedic tone the film has compared to the previous two, not to mention the Shrunken Head added to the Knight Bus.
The excision of the explanation of the identities of Moony, Wormtail, Padfoot, and Prongs, which confused many moviegoers who hadn't read the books. Especially since it would have been relatively simple to slip into Lupin's final scene.