Harry Potter’s back, and the good news is he’s better than ever. Mexican director Alfonso Cuarón takes the helm, turning in a darker effort than the previous films, as Harry and his friends move into adolesence.

The story begins, of course, at the Dursley home, where Harry is becoming increasingly resentful of his mistreatment. When a visiting aunt (Pam Ferris) provokes him, Harry loses his temper and inflates her like a balloon in the film’s most whimsical moment.

Returning to Hogwarts, Harry finds that the murderer Sirius Black (Gary Oldman) has escaped from prison and is thought to be coming after him. As a result, the prison guards -- the soul-sucking Dementors -- are roaming Hogwarts, and they seem to have a particular effect on Harry.

As in the previous films, the children are supported by an exceptional array of British acting talent. Alan Rickman has a lot of fun reprising his role as the sneering Professor Snape, and Robbie Coltrane is routinely excellent as the genial Hagrid. Emma Thompson and Timothy Spall get to wildly overact in roles that will probably amuse children, and Michael Gambon takes over as Dumbledore, giving the character a warmer, less magisterial feel than Richard Harris.

As for the children’s performances; well, they are improving, although Daniel Radcliffe and Rupert Grint are still completely outshone by Emma Watson, who makes the most of the series’ best part in the quick-witted, determined Hermione. She gets more to do this time, as well as the film’s best line, when in a moment of time travel she sees herself in action and asks, “Does my hair really look like that from the back?”

Harry Potter is all about magic, of course, and Cuarón doesn’t disappoint. The action sequences are genuinely exciting, in particular a storm-lashed Quidditch game and a wonderful epic flight on a Hippogriff, a bizarre creature that seems to be half-horse, half-pigeon. Overall, the film looks great, with a darker, grainier feel, although the special effects do seem a little homely and second-rate when compared with, say, the Lord of the Rings.

However, despite some impressive scenes, the story loses momentum at points, which is probably indicative of the challenge faced by screenwriter Steve Kloves, as the third book is a hundred pages longer than the first. At one point in particular the film tries to tie up a number of plot strands, and ends up being simply baffling.

Nonetheless it’s an extremely entertaining film, the best of the series so far, with enough action, humour and suspense to please adults and children alike.

(Released by Warner Bros. and rated "PG" scary moments, some creature violence and mild language.)