There is something wonderfully counter-cultural about the Harry Potter series. Mainstream mass entertainment product is increasingly aimed at people whose faculties of concentration and memory have been dulled by the sensational junk they have already consumed. But the Potter films, like J K Rowling's books on which they are based, have gone in the opposite direction. They get longer, slower and more complex (and therefore duller for non-believers), and expect ever more knowledge and effort from their audience.

That the franchise is now seven films long, and will reach eight when the final episode comes out next year, shows that treating even young people with respect for their intelligence can be a money-making proposition - perhaps a startling notion for an industry that prefers to underestimate the public.

As the original audience has grown older, so have the characters, and with them the sense that the world may not be a place of happy endings. But the thing that makes this seventh episode unique is that Hogwarts does not appear in it at all. For most of the film Harry, Ron and Hermione are on the run, sometimes in the countryside, sometimes in the now threatened "muggle" world, and at one point inside the Ministry of Magic, which has a decidedly fascist feel.

It is not clear if director David Yates and writer Steve Kloves realised the risk they were taking by having the three main characters drop out of school and leave its familiar, if unsafe grounds. The glorious Gothic boarding academy is a character itself, and the source of much of the films' charm. You miss it here. In its stead are some beautiful British rural locations - desolate beaches and wintry forests - where the three main characters find themselves as they flee the agents of the Dark Lord and search for the "Horcruxes", the magical devices that hold the key to his destruction.

There is furious action at the beginning and the end, with the usual clever effects, but much of the film is taken up by arguments and angry silences as three 18-year-olds share a tent on bleak hillsides, their relationship undermined by the evil locket they are carrying and by unspoken sexual rivalry. Unfortunately, the long periods of talk highlight the weakness of the young leads compared to the established British stars in supporting roles (Bill Nighy and Rhys Ifans join their number here).

Daniel Radcliffe, as Harry, is burdened by an under-written, two-dimensional character, but he is simply not interesting to watch on screen. Rupert Grint as the oafish best friend Ron is as tiresome as ever. Only Emma Watson as Hermione has become an actor capable of suggesting a more than minimal range of emotion. It makes it more obvious than ever that Hermione not Harry should be the hero. She is the cleverest, the best at magic and the most emotionally intelligent. Harry is the hero only because he is fated to be the "One", and perhaps because you need a male central character to pull in both boys and girls.

The Potter audience understandably prefers the decor of the pre-plastic wizard universe to shiny, metallic modernity. Its cottages and cosy burrows (as always, much of Potter universe is "borrowed" from Tolkien) suggest a richer, deeper, though darker old world.

But there is one less pleasing aspect of the weird Edwardian-medieval magic world: both Kreacher, the long-nosed, house elf, and Mundungus Fletcher, the thief with an East End accent, evoke traditional Jewish stereotypes that some might find objectionable.