Last night’s visit to see Harry Potter and the Half-Blood Prince at an IMAX on the other side of London just to see it on opening night with 3D scenes has to tell you how much I generally enjoy both the films and the books. But I like to think I’m a fair fan; I understand the difficulties in transferring a massively complex plot into a concise film that isn’t a turgid bum-number. Unfortunately, this is the second time I feel David Yates has slightly missed the mark.

With Harry Potter and the Order of the Phoenix, I blamed the lack of Steve Kloves. And indeed H-BP sees far better dialogue and far more natural interaction between the teenage characters. Harry under the influence of luck potion Felix Felicis is a joy to behold – finally a real teenager, full of mouthy chutzpah. But now I can’t help feeling part of the problem lies with Yates; although he consistently turns out stunning visuals and encourages improving performances from his key cast, he’s also got a little carried away with the editing.

There’s certainly fat to trim from the books, and some of the changes were judicious. The first ten minutes – the 3D scenes, if you’re watching that version – are exciting and visually breathtaking. They quickly set the tone of urgency but also raise the CGI bar, which means a variety of totally unnecessary devised set pieces – a random race through the long grass against Fenrir Greyback among them – have to be shoehorned in to maintain the pace.

Let’s look at the positives. The flashy good looks I’ve already mentioned, but there are other gems here. Emma Watson has finally invested real character and humour into Hermione. Sadly, Harry is still on the bland side, except when acting up under the influence (see above); Rupert Grint, however, blithely holds his own as the most vibrant of the three, bringing warmth to Ron’s innately cartoonish personality. A star is surely born in Jessie Cave who delivers a fabulously insane comic turn as Lavender Brown.

Indeed, thanks in large part to Cave’s psychotic gurning, the much-mooted romantic comedy elements do live up to expectations. Hormones are running high, and there are a few opportunities to puncture the relentless gloom with genuine laughs.

Tom Felton and the ever-brilliant Alan Rickman are also allowed room to breathe in this installment, and it’s a pleasant change from just watching them alternately sneer and loom. Felton in particular takes every opportunity to give Draco Malfoy a proper, three-dimensional outing at long last. The whole vanishing cabinet episode is nicely summarised to take out a lot of waffle from the book, which lets us get straight to the heart of the increasingly desperate boy that much quicker. In addition, Helena Bonham Carter’s increasingly deranged Bellatrix Lestrange is a joy to watch, cavorting evilly like one of the demonic creatures in that animated 80s take on The Lion, The Witch and The Wardrobe.

Yet somehow, something is lacking throughout. The series can now be deemed completely incomprehensible to anyone who hasn’t read the books, which rather knocks the wind out of the sails for many viewers. In the book, I shivered with horror when spotting Marvolo’s ring on Tom’s finger in Slughorn’s memory; in the film this key moment is completely missed thanks to half-baked and incomplete exposition. My husband, who has never read any of the books, has happily watched the films so far but was quite at a loss to explain much of what went on in this one. Since a large chunk of key plot development is removed, there’s a thumping great gap in Harry’s knowledge at the end of the film; I’m curious how they’re going to fill that hole without a couple of clunky shovels.

Finally there’s the matter of Dumbledore. I have never been thrilled with the casting of Michael Gambon, who interprets Dumbledore with far more aggression and far less humour than the late Richard Harris did. Dumbledore’s fits of sudden steeliness and temper are startling on paper because they emerge from behind an apparently seamless veneer of twinkly good nature.  Gambon’s leaden-toned, grumpy wizard (who quizzes Harry on his love life – most unlike Rowling’s Dumbledore) is hard to like and only grudgingly respected. My husband described the performance as ‘soporific’, and I can’t really disagree with him, although there is a brief moment towards the end where, weakened by a murky potion, Rowling’s Dumbledore and Gambon’s suddenly seem to become one.

As a film for the fans, H-BP only partly succeeds in recreating some of the creepy tone of the original book. As a film for those who have not read the books, it gets mired in the plot labyrinth and often comes unstuck. Yes, it’s a beautifully crafted piece with some really excellent performances, but in the end cannot really be more than a three-star effort.