I started my review of The Prisoner of Azkaban by stating that it has long been my answer to the question "Which is your favourite Harry Potter film". Rewatching The Order of the Phoenix, however, stirred up some long-forgotten memories and feelings, as a result of which I will have to revise my answer. This is my favourite film (and book) in the franchise. How on earth had I forgotten that?!
Thematically and cinematically, The Order of the Phoenix is not as tight nor as clever as Azkaban, but the emotional impact it hits me with is far greater. Dolores Umbridge is just a remarkably clever antagonist, walking a tight line between fantastical witch and authoritarian bureaucrat, the latter making her actually relatable to the viewers' own lives. It is this relatability that I feel makes The Order of the Phoenix so much more than the sum of its parts.
Objectively, the plot is very much a bridge, moving the viewer away from a Hogwarts that is beset by annual monstrous threats but ultimately very disconnected from the wider Wizarding world in which it is set, towards a Hogwarts that is very clearly influenced (and influencing) an entire civilisation. This transition is a requirement for the over-arching plot to develop, for the impact of Voldemort's return to be felt, and for the (now teenage) main characters to begin their first steps into adulthood. In the same way that everyone's world expands rapidly during their teenage years, as you begin to grasp the immensity and subtleties of the society you live within, so Rowling forces the world of Hogwarts to expand. The effect is very subtle, but when combined with an almost non-magical threat that could so easily exist in our own world (blood quills aside), the result is a story that feels deeply personal.
The stakes, of course, have also been raised and the repercussions are felt very deeply. The division within the wizarding world over whether He-Who-Must-Not-Be-Named has actually returned and, therefore, who to trust – the government or one of the most respected individuals in their society – feel real, both inside and outside of the school itself. Core characters begin making irreversible decisions, with the Weasley twin's effectively choosing expulsion or the (arguably darker) impact of school kids having to train themselves for war, effectively choosing a side in doing so.
Ultimately, others may not feel as strongly about The Order of the Phoenix as I do, but it clearly speaks to something buried deep within me. The underlying themes of racism, particularly with the introduction of "half breed" characters such as Grorp and the increasing feud of the centaurs, are very cleverly woven into the plot. They feel neither forced nor centre stage but, unlike The Goblet of Fire, the filmmakers have managed to make them fit. Sure, a lot has still been cut and even more has been simplified, but the result is arguably the most internally consistent film in the franchise.