The End: "Harry Potter and the Deathly Hallows Part 1"

"Which creature was sitting in the corner of my office the first time Harry Potter visited me?" The question is asked by David Thewlis's Remus Lupin to establish whether Harry Potter is who he says he is as the war against the dark forces in J.K. Rowling's universe steps up, but it might equally be used to determine whether cinemagoers are in or out, at this late stage in proceedings. Half an hour into HP7a - the first part of the final instalment - and it's become evident the series has descended into the interminable fans-only trivia and juvenilia it has always threatened to. This is supposed to be the big climax; instead, we're offered a series of footnotes. The tale of Beedle the Bard (copies still available in all good bookshops); the revelation of where Dobby the House Elf has been hiding all these years; a diversion to the scene of Potter Sr.'s final stand. Rowling - and the producers, and director David Yates, taking a third crack at the franchise - is dotting the is and crossing the ts and making sure everybody's on the same page here, no matter we're supposed to be watching a film.

I had a grudging respect for the previous instalment, 2009's Half-Blood Prince, for the manner in which it appeared to overcome its production difficulties to arrive at the functionality that has been the mark of the better entries in this series; it was during this penultimate film - first intended for release in 3D, released in 2D, and sometimes straining to attain anything like monodimensionality - that my patience snapped and I threw in the towel altogether. It's a double shame: firstly, as I haven't read the books - and thus have the suspense advantage of not knowing who lives and dies - and secondly as Deathly Hallows would appear to be the one where Rowling finally had the confidence to abandon the comforting and predictable formula that underpinned previous instalments: that seasonal structure of suburbia-train-Hogwarts, then arsing around for a while until an actual plot can be happened across. The school that has sought to nurture and protect our heroes for so long is very definitely out: Ron, Harry and Hermione are on the run from the word go, pursued by Voldemort and his forces, and on paper at least, everything seems to be up for grabs.

On celluloid, however, it's a different matter. You have to wonder how many Potter films Yates - now, presumably (and absurdly), the most bankable director in the world - would have to make before he found anything like a satisfying rhythm in this material: 7a is a feature that hops, but mostly plods, between set-pieces in which it's not always clear why we're here or what, precisely, is at stake. In Yates's defence, it's not entirely his fault: this one is plainly the worst adaptation of a Potter book yet, as though over-qualified screenwriter Steve Kloves had himself thrown in the towel. If you are going to have your characters hyperventilate on a quest for something or someone known as a "whorecrux", then sooner or later you are going to have to explain what (or who) the damn things are to that percentage of viewers (however small) who haven't read the books. Similarly, having somebody rush in to tell us characters we've only just been introduced to have died off-screen, simply to raise the narrative stakes (or to avoid shooting effects-heavy death scenes), will always seem like a dreadful cheat.

Of course, you could continue to praise the consistently high standard of production design, and the continuing project to tick off those few British character actors who haven't as yet appeared in a Potter film: here, Peter Mullan (hopefully opening up a line of credit for future directorial outings), Rhys Ifans, John Hurt and, most unexpectedly, Graham Duff - the polymorphously perverse Brian from TV's Ideal - as one of Voldemort's Death Eaters. But in Deathly Hallows' two-plus hours, there are precisely two amazing effects: one the work of computers, the other I can't even begin to explain, both seeming to stand in some way for the failings and limitations of the whole.

The pixellated wonder is spent early on, as Brendan Gleeson's "Mad Eye" Moodie transforms several volunteers into replica Harrys, in order to allow the real thing to make his escape from the Dementors. The other wow, the inexplicable one, is how the series' three lead performers - now young adults, as their groomed and glamorous appearance at each passing premiere has only come to demonstrate - have continued to retain on screen a convincing patina of adolescence. Whatever spell has been cast on them - juvenilia perpetuum? - it's started to rub off on their elders, too. To penetrate the darkened halls of the Ministry of Magic - a no-fly zone for boy wizards - Ron, Harry and Hermione are obliged to assume the form of adults (Hermione's clearly inhabiting Sophie Thompson: another tick) who nonetheless speak with the voices of Messrs. Radcliffe, Watson and Grint.

The grown-ups in Deathly Hallows - and in this, we'll include the man behind the camera, allowed to exhibit no discernible personality of his own - are employed as hollow dummies, mere conduits for childish whims; this particular form of ventriloquism is eerily similar to the manner in which these books have been brought to the screen. The film's vision of terrifying conformity - the aforementioned Ministry, with its rows of desk-bound clerks Xeroxing Mudblood propaganda documents - is as nothing set against the terrifying conformism of the film itself. Actors mouth their lines; directors are forbidden from imposing themselves. Everyone bows before Harry Potter, even poor Dobby, who's no sooner announced himself a "free Elf" than ended up a sacrificial lamb. (Half-Blood Prince at least drew towards its close with the death of a human being; Deathly Hallows asks us to mourn for a computer effect, and heaven knows how many more of those this franchise has left.)

It's too late for a corrective, of course - the film has already taken over the multiplexes and invaded the global consciousness - but we might at least give pause to wonder who, save the Warner Bros. accountants, is actually winning this bloody battle. The first Potter movie, Philosopher's Stone, emerged in late 2001, mere months after the most devastating attack on Western values suffered in our lifetime, and it seems likely the series will come to an end at a moment of acute financial depression. Sure, the films have provided a certain bright-eyed, bushy-tailed distraction over the decade, but nothing really appears to have changed for the better in that period, in both Rowling's fictional and our real worlds. As we leave Deathly Hallows Part 1, everybody's still running around with their wands in their hands, and the saga looks no closer to reaching a happy or conclusive ending - there's a metaphor for something there, I'm sure. Part 2 will follow in July 2011, and doubtless finance Warners' next round of remakes and comic-book adaptations, yet this franchise badly needed to end here. Plainly put, we all need to grow up now.

Harry Potter and the Deathly Hallows Part 1 is showing nationwide.