The question I would ask, for a start, is whether Harry Potter and the Prisoner of Azkaban is chiefly a Harry Potter movie, or chiefly an Alfonso Cuarón movie. This is, of course, dumb as fuck: there are people who have seen and worshiped and idolised Prisoner of Azkaban who probably haven't even heard the titles of the director's other six features, and would possibly drop dead of mortification if they ever accidentally stumbled upon the sex-soaked Y tu mamá también. That being said, it's awfully easy and darn near obligatory to suggest that the eight-film franchise stretching from 2001 to 2011 breaks into two very different phases: the first two films, Harry Potter and the Sorcerer's Stone and Harry Potter and the Chamber of Secrets, are fundamentally different than the six movies that followed them. And this shift, which I think unambiguously favors the latter six, can be attributed to Cuarón as readily as to any other individual. So perhaps the trick isn't think of Prisoner of Azkaban as the one impersonal film that Cuarón made, but to think of the latter Potter movies as Cuarón films that happen to have been directed by other people.

In at least one respect (besides the fact that it's his only mega-budget studio film), it is a clear outlier: it is the only feature in the director's career not shot by the great Emmuanuel Lubezki, replaced for reasons unknown to me by Michael Seresin (who would later shoot Cuarón's segment in the omnibus Paris, je t'aime). And Seresin is not at all without talent, and Prisoner of Azkaban is gorgeous and deeply characteristic in its visuals, but it's not, like, Lubezki-gorgeous. That's still enough for it to have ended up directly influencing the visual style of every one of the subsequent Potter films: Harry Potter and the Goblet of Fire, directed by Mike Newell and shot by Roger Pratt, copies it almost exactly, and while the four films directed by David Yates have three unbelievably talented men shooting them (Sławomir Idziak, Bruno Delbonnel, and Eduardo Serra), using three distinctly different and personalised aesthetic approaches, all of them are largely within the wheelhouse that Cuarón and Seresin piloted in this movie, viz. sparkly black children's fantasy that has one foot in a ghost story and one foot in a beloved childhood picture book of fairy stories. Compared to the blandly over-lit and vigorously unmagical approach that director Chris Columbus and cinematographers John Seale and Pratt used in the first two movies, this isn't just a revelation; it's more than that. Prisoner of Azkaban had to prove that a decade-spanning franchise guaranteed to be a gigantic hit because of the brand name could be more than financially successful; it had to prove that there could be thoughtfulness and artistry applied to the material, that it would actually be possible for these movies to be nice to look at and fun to watch, two phrases which apply in no degree to either Sorcerer's Stone or Chamber of Secrets.

Nearly ten years past the commanding success of Cuarón's rather drastic re-conceiving of the material, it's hard to remember how bold this was at the time: the director of a wildly well-received travelogue about sex and politics in Mexico (though it's a matter of record that the reason he got the job was his sparkling A Little Princess) being given the keys to the biggest moneymaking machine in the world, what with Peter Jackson's Lord of the Rings trilogy having wrapped up the prior year, and instead of copying the model of his predecessor, pulling at damn near everything and starting from scratch with all of it. The quantum leap in the lighting, and the encroaching gloom of the atmosphere thus generated, are one obvious example. The fact that he freed up his young trio of stars to wear street clothes almost the whole time instead of their twiddly school uniforms from the first movie is another one, that frankly has just as much impact: instead of seeming like kids playing dress-up on great big sets, the movie is suddenly about actual young people. The full-on embrace of horror is another: J.K. Rowling's source novels are chock full of the normal fantasy monsters and things going bump, but the movies as a rule have edged back from that, and only Deathly Hallows: Part 1 can be compared at all to the gleeful embrace of genre technique that Cuarón explores here - it's also worth pointing out that nothing in his career before or since much resembles this, either. The results pay off splendidly: an early sequence set in a park in the dead of night, with little beads of dew backlit like the teeth of some unseen demon, and a somewhat later scene of a wraith-like Dementor reaching its skeletal hands at the heroes, are still among the very best moments of the entire franchise, and the latter might still be the best.

It all goes to prove that you can do visual and tonal darkness, mixed with gobsmacked fantasy (something else Cuarón and Seresin achieve that the previous films did not: make the Hogwarts School of Witchcraft and Wizardry actually look like the splendid carousel of wonders that the scripts insist on it being), and make a film that's tremendously appealing and fun and not at all too scary or glum, and the fact that any adult has ever once had something kindly to say about the Harry Potter film franchise can ultimately trace back to that incredibly important achievement.

Thank God for it, too, because outside of Cuarón's incredible accomplishment, Prisoner of Azkaban has some severe problems, starting with its script, which I genuinely believe to be the worst of all eight films. Other than Chamber of Secrets (which paid for it by being the most protracted and deathly dull of them all), each of the Potter films suffers from too much compression and rushing, mercilessly sloughing off incidents, subplots, and even entire characters, in the interest of making Rowling's doorstops reasonably contained in a running time that anybody would be willing to sit through; not a damn one of them actually manages, after all that, to tell a completely functional story. Prisoner of Azkaban, I am convinced, is the least-functional of them all: in the first hour and a half, it achieves some measure of coherence but not momentum, clanking through the worst kind of "this happened, then this happened, then this happened" anti-narrative, consisting of nothing but a long chain of scenes that are connected solely because they all involve Harry Potter (Daniel Radcliffe), Chosen One of the British wizard world. In the remaining 50 minutes (resulting in the series' first entry to make it in south of two and a half hours), momentum is achieved at the cost of sense; from the very moment that the first of many Big Reveals takes place, the film descends into a maelstrom of tossed-off developments and undernourished backstories, hitting the bare minimum of plot points required to have the semblance of form at all (it doesn't help that, even as a novel, Prisoner of Azkaban is unique in not really possessing a "confilict" as such). The only thing that compares is the failure of Half-Blood Prince to satisfactorily clarify who the half-blood prince, in point of fact, is; and that's just one minor plot point. Prisoner of Azkaban doesn't really clarify two entire acts.

The other big issue is the acting: over the course of the franchise, Radcliffe generally got better, while Emma Watson (as the smug intellectual Hermione Granger) and Rupert Grint (as lovable schmuck Ron Weasley) both got worse, and it's in this film and the very next one that they averaged out to the lowest overall capability: a lot of super intense staring and shouting from Radcliffe, a lot of pedantically over-delivered lines from Watson, and I don't know what the hell Grint was doing in this movie. Moving on to the huge panoply of British character actors filling in the corners, some are good (David Thewlis as a Big Secret-keeping professor), some are amazingly good (Gary Oldman as a Big Secret-keeping escaped convict; Emma Thompson as a nutty, pretentious clairvoyant with, alas, no secrets of any size). As is common with these films, several are given hardly anything to do - the descent of Maggie Smith into overqualified set-dressing began in earnest here - and Michael Gambon, stepping into the shoes of the late Richard Harris, was at his very worst as the kindly, mysterious Dumbledore, trying much too hard to evoke something of Harris's characterisation in his own performance and missing by quite a lot.

That being said, the film's chief failures are dramatic, not cinematic, and as escapist fantasy spectacle, there's much to love: John Williams's final score for the series is his best, much deeper and more interlocked than the auto-pilot collection of Spielbergisms he'd used twice before, the new sets (especially the quirky little town of Hogsmeade) designed by the inexhaustible Stuart Craig are more playful than before, the CGI is pretty great across the board. Except for the werewolf, because for whatever reason, CGI werewolves never work.

And it's all shown off to beautiful effect by Cuarón, employing his trademark tracking shots (though none of them very long) to dance around the sets and explore them (the opening shot, a grand track in and then track back, gets us off on the right foot: the camera is there to sweep us into and around the movie), relying on a motif of silent-movie irises to give the film a much-welcome sense of wide-eyed storytelling, incorporating a few pitch-black jokes about harmlessly flying creatures being violently killed, and even given the three-way hug that was so crucial in Y tu mamá también a cameo. It is closer to his least complicated and rewarding filmmaking than otherwise, and like many gifted filmmakers who primarily work with humans, he seems to have been unsure what to do with CGI beasts that weren't there yet. But all in all, the filmmaker who made A Little Princess such a playful bit of fantasy and deeply respectful depiction of children is unmistakably the filmmaker behind Prisoner of Azkaban, even with all the pressures and studio tinkering that comes with making a massive-budget adaptation of a fiercely protected brand name. Whatever failures it has, it's arguably the most fun Harry Potter film to watch: inventive, quick-moving, playful, beautiful.