Professor, just so you know I don't think that map always works. Earlier it showed someone in the castle... someone I know to be dead.

No 471 - Harry Potter and the Prisoner of Azkaban
Director - Alfonso Cuarón

So, I didn't have to sit through the first two films, I could move straight to book 3. This is the only Harry Potter film to appear in the top 500 and I think the main reason it does so is because it changes the films.
It is not a massive revolutionary change. After all Cuarón was going into a filmic universe which had been set up for two films, and the world of Harry Potter is defined by J.K Rowling and defended by legions of frankly terrifying fans. However there were some important changes. The main one is that this is the film where the series started focusing on the characters rather than the magic.

I always felt that Chris Columbus was trying to razzle dazzle us with his view of Harry Potter's world, that each moment of the film had to feel like a set piece full of spectacle and wonder and well... magic. Here is all feels considerably more understated. People use magic to quietly stir their coffee, to light candles or to make interesting animal noises. The magic is not in the forefront, and this means we can actually begin to really care about the characters.
This is helped by the second big thing that is introduced in this film, the idea that these characters are contemporary children. So, gone are the robes and instead we have children walking around in hoodies and jeans and other things that young people wear. It makes sense. It feels right. Whereas in the earlier films (and indeed in the books) you could kind of forget that this was the here and now and instead immerse yourself in the quaintly Victorian Wizarding world... here you begin to notice more and more that things are happening NOW. It is a theme that is taken and expanded on more and more within the later films, see Order of the Phoenix's flight through London or Half Blood Prince's attack on Millenium Bridge. I like the mix of our world with the wizards. By sticking too much in Hogwarts you end up basically in another fantasy world, and oddly... that dulls the magic.

There are then the smaller new touches. I really like the clock tower that only seems to be in this film. It means that large parts of Hogwarts have exposed clockwork, which adds a really nice touch. Best of all is the stonking great pendulum in the middle of the entrance hall. It means the students have to duck and weave to avoid getting smacked by it - it looks cool, but it is a health and safety nightmare. Considering Hogwarts is a SCHOOL there seems to be some very lax health and safety rules. I mean during a game of quidditch, THE SCHOOL SPORT, one player is ON FIRE and the other gets ELECTROCUTED. What do they tell the parents? Just because you have a super awesome magic hospital wing doesn't mean you can totally disregard the safety of children.
Whilst we're on the school side of thing, how weird is Slytherin? How come there is an entire quarter of the school that are allowed to fuck about and be pompous and get people into trouble and bully the other children. Then you can't do anything because they're Slytherin. How the hell can that even be an excuse.

Hogwarts, as a school, is a poorly run disgrace. I blame the headmaster!

Which neatly brings me back on topic with the next new thing in this film. Michael Gambon. In the first two films, Richard Harris played Dumbledore as a very softly spoken, wise, frail and impossibly old wizard. It worked for the earlier films because the cast were so young, they needed the hand holding, but he seemed quite a dull character just because he was so kindly and old. Suddenly in barges Michael Gambon. Far more energetic, far less hairy slightly west country with hints at Irish and with a bubbling undercurrent of danger.
My little sister, the obsessive Harry Potter nerd, doesn't like Gambon's portrayal because he seems too angry, too scary. I love it. Dumbledore is meant to be an incredibly powerful wizard, who has fought some incredible battles and who has permanently been up against criticism for his unorthodox ways. Gambon encapsulates that. His Dumbledore is a man with masses of time and compassion for his students but also with about a million things running through his mind at the same time. He seems permanently busy, frequently on edge but clever, understanding and fair. That is the important thing

The other teachers, as usual, don't get much of a look in. This is why I see Harry Potter as a mixed blessing. It really collects some amazing British actors. Then gives them about 4 lines as it focuses on children who (still) can't bloody act. Rupert Grint and Daniel Radcliffe get gradually better but I think Emma Watson will be wooden forever.
This film adds Michael Gambon, Gary Oldman, Timothy Spall, David Thewliss and Emma Thompson (to name a few) into an already swelling cast list. Yet, dispite these phenominal actors (and the later inclusion of greats like Helena Bonham Carter, Brendan Gleeson, Ralph Fiennes, Jim Broadbent) none of them get the chance to act... they just are sort of there. Offering exposition for the kids.
Even then, the film messes up.

At one point, Harry Potter is given the Marauder's Map. A sneaky parchment with a complete map of Hogwarts. It even marks every person in the building and where they are. How very useful. The map has a whole load of back story. Read it here. It introduces Messrs Wormtail, Moony, Padfoot and Prongs. However the film never explains who they are. It never explains why Lupin and Sirius have heard of the map and know how to use it. The importance of the nicknames are implied but never REALLY mentioned.
Plot wise, this is the film's biggest weakness.
But, the brilliant ending more than makes up for it. Playing like a version of Time Crimes for kids... Harry and Hermione use time travel to try and save the day... finding themselves directly responsible for things that happened earlier on in the film. It is a beautiful bit of playing with paradox and nonsense like that. I love it as a touch because it is so cleverly done and I do appreciate it when Time Travel is cleverly done.

I'm losing structure here, I have two more things I want to talk about but no way of linking them together.... so, quickly:

I really like the werewolf in this film. The transformation is pretty standard. Using a lot of the bone growing pain that comes from American Werewolf in London and has been used in everything since. What I like is that Lupin is more Were than Wolf. He doesn't just turn into a big dog... instead he turns into a kind of ape dog. With long orangutan arms and an awkward loping run. It is a great reinvention of the wolf man, one that puts as much focus on the Man element as it does on the Wolf element.

Finally... I like Trelawney's prophecy. I have to file J.K Rowling in the same camp I file Russel T Davis. In that fundamentally I find their writing quite annoying but the way they set stuff up is amazing. Harry Potter stories have so much going on, and it is so refreshing when you realise that all these little things are important. Are leading up to something. Something big.

It is just a shame that the big thing is never as big as you pictured it.