Prince of Persia: The Sands of Time, Mike Newell, 115 mins (12A)Heartless, Philip Ridley, 113 mins (18)

Never trust a blockbuster with a colon in the title

When did watching a summer blockbuster become so much like poring over a quantum mechanics textbook?

In my young days, before every big-budget action movie was derived from a comic, a computer game, a toy range or a theme-park ride, you could watch Star Wars or Ghostbusters and have a pretty strong sense of what was going on. But did anyone understand the byzantine plotting of Pirates of the Caribbean: at World's End or Transformers: Revenge of the Fallen? Even the titles are hard to get through.

A case in point is Prince of Persia: The Sands of Time, which is just as convoluted as you'd fear of a film produced by Jerry Bruckheimer, based on a series of video games, and saddled with a colon in its title. It opens with a set of captions, then a voiceover to fill in yet more information, and finally a flashback to the hero's childhood – three surefire indicators of a plot-clotted ordeal to come. In the flashback, the hero is an orphaned urchin who's adopted by the ruler of ancient Persia. Years pass, and the lad grows up to be a musclebound, English accented, permanently unshaven Jake Gyllenhaal. When he's framed for his adoptive dad's murder – a crime which could have something to do with the dead king's brother, Ben Kingsley – he goes on the run with an eligible princess, Gemma Arterton, who looks even less Persian than Gyllenhaal, however much orange fake tan she's slathered on.

Then Gyllenhaal discovers a mystical dagger which allows its bearer to rewind time by a few seconds and thereby have a second stab at sticky situations. You can see how handy such a device might be in a video game – or in reality, should you ever be caught calling someone a "bigot" – but in the film the dagger is used so sparingly it might as well not be there. It's just one of the many elements that the screenwriters have squeezed in, including some super-powered assassins and an ostrich-race promoter (Alfred Molina, the film's one bright spot), and topped by some arbitrary mythology about a subterranean hour-glass created by the gods to destroy the world.

There's so much of this stuff to plough through that the film has been edited down to confetti-like snippets. Gyllenhaal escapes from his enemies about once every minute, undergoing so many reversals of fortune that he's lucky not to get whiplash, and yet it's this very hyperactive pacing that neutralises any potential excitement. Gyllenhaal/his stunt double/his computer-generated doppelgänger may do a lot of leaping across rooftops and swinging from ropes, but it happens so fast that by the time you've registered that he's in danger, he's nipped right out of it. Even a sky-filling sandstorm passes by as if it were a light breeze. There's also no breathing space for comedy or romantic chemistry to develop – a grievous waste of the director's talents, given that Mike Newell also made Four Weddings and a Funeral. If he remade it today, it would probably have to be called Nine Weddings, Five Funerals: a Cryptic Prophecy about a Vicar from Another Dimension.

Philip Ridley, the love-him-or-hate-him British auteur who wrote and directed The Reflecting Skin and The Passion of Darkly Noon in the 1990s, has been busy with plays and children's novels in recent years, but he returns to the screen with Heartless, a philosophical horror film set in east London. Jim Sturgess stars as a photographer's assistant who's cripplingly self-conscious about the heart-shaped birthmark on his face.

At first the film shuffles along gloomily – a downbeat "Broken Britain" jeremiad, in the vein of Michael Caine's Harry Brown, with the addition of some Dr Who monsters. But halfway through it finds a black sense of humour, and becomes a crackling Faustian comedy which features Joseph Mawle as a cockney Satan and Eddie Marsan as his businesslike right-hand man. Heartless still has more ideas than it knows what to do with, but they're just about balanced by its jokes – and its heart.

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