Harry Potter and the Half-Blood Prince, David Yates, 153 mins, (12A)Frozen River, Courtney Hunt, 97 mins, (15)

Don't expect a storyline as teen romances fail to spark and our speccy hero takes a back seat to his arch rival. Still, production design is wondrous ... and there's always the Quidditch

In the final scene of the new Harry Potter film, our speccy hero looks back at his latest adventure and laments that "it was all for nothing". He makes a fair point. Harry Potter and the Half-Blood Prince is the sixth episode in a series of eight (JK Rowling's seventh book is getting two films to itself), so it was inevitable that it wouldn't end with a satisfying full-stop. But at least the first few films in the franchise had their own stand-alone stories, whereas this time all we get is a small piece of a large jigsaw.

It's still a colourful piece, mind you. Although HP6 doesn't have much fun or humour compared to earlier instalments, its production design is wondrous to behold, and it has the requisite Quidditch matches, hamming British actors, and sprinklings of incidental magic: a baby dragon roasting chestnuts, books floating back to their proper places on the library shelves. What it doesn't have, however, is a plot.

The opening promises a no-holds-barred clash between good and evil on the streets of London, but before long we're back at Hogwarts where, as ever, there's a new teacher in the staff room. He's Horace Slughorn (Jim Broadbent), a rumpled, tweedy old buffer who teaches his charges how to brew potions. Harry (Daniel Radcliffe) does particularly well at these lessons because his dog-eared textbook has been annotated by a former pupil, the Half-Blood Prince. This, of course, is the cue for Hermione (Emma Watson) to investigate the mysterious alumnus's identity – or so you might assume. But in a break from the usual turn of events, Hermione doesn't find out anything, and the question appears to have no bearing on the story, anyway. It was all for nothing, indeed.

Ron (Rupert Grint) has even less to do than Hermione, and Harry himself faces danger only because he's dragged into it by the unhelpfully cryptic Professor Dumbledore (Michael Gambon). I'm inclined to think that if Hogwarts' abstruse headmaster had ever sat down with his highly qualified teaching body, and told them everything he knew about Voldemort, they'd have sorted out all their problems with the Dark Lord before the lunch bell.

Most of the film is taken up with scene-setting for the final two instalments, plus some teen romance which has the characters pairing off with all the passion of children who have been told to sit on an aged relative's knee for a family photo. It's possible that these sequences might have had a bit of oomph if the young actors were more natural, but the only one of them who's in the same class as the grown-ups is Tom Felton, who plays the tortured, resentful, and shockingly tall Draco Malfoy.

The curious thing about HP6 is that it's Malfoy, not Harry, who goes creeping around the school corridors after lights out, carrying out a secret mission and struggling with his destiny. Maybe the screenplay should have focused on him instead. As it is, it's the first Harry Potter film that could have done without Harry Potter altogether.

Frozen River has a meagre budget, a subdued tone, a modest running time and an almost unknown cast, but it packs a remarkable number of issues, ideas and twists into what looks at first to be a depressing, albeit timely indie drama about life on the brink of destitution.

Its heroine, Melissa Leo, is only just making ends meet in icy upstate New York. Effectively a single mother, now that her husband has run off with all their savings, she lives in a trailer, and raises two sons on a diet of orangeade and popcorn.

So far, so earnest and sobering, but then Leo stumbles on a way to make a quick buck by smuggling illegal immigrants over the border from Can-ada in her car boot, and the film accelerates into a tightly plotted crime thriller, without ever losing its initial rough-edged realism.

It makes a change from all the films we've seen recently about Mexicans crossing the United States' southern border, usually starring Tommy Lee Jones. Courtney Hunt, the writer-director, casts a shrewd eye over illegal immigration, and spots plenty of ironies. Considering how badly Leo's own American Dream has turned out, she finds it hard to believe that anyone would pay thousands of dollars to get into her country. Meanwhile, her partner in crime – although Leo keeps telling herself that she's "no criminal" – is a Mohawk woman, so her community sees Leo as a recent immigrant herself.

Another director and a bigger budget might have given the film the momentum it lacks, but Leo's performance and Hunt's screenplay both richly deserved their Oscar nominations.

Also Showing: 19/07/2009

The Informers (98 mins, 15)

Flimsy Bret Easton Ellis adaptation set in Los Angeles in 1984, with Mickey Rourke, above, just one of the stars. A newsreader (Winona Ryder) has an affair with a studio executive (Billy Bob Thornton) whose wife (Kim Basinger) is sleeping with the best friend of her drug-dealing son whose model girlfriend is staying with a rock star .... etc. The moral seems to be that endless, mindless self-indulgence doesn't make for a very fulfilling lifestyle, after all. Who would have thought it?

Burma VJ (84 mins, (12A)

The civil unrest in Rangoon in 2007 was reported around the world, thanks largely to the bravery of Burmese undercover video journalists (VJs). This gripping and important documentary uses their footage to tell the full story of the uprising, and the VJs' pivotal role.

Kisses (75 mins, 15)

Micro-budget urban fairy tale with a boy and girl roaming nocturnal Dublin.