On paper, Pompeii oozes potential.

There's the chance for a good old-fashioned disaster movie, with lashings of CGI-generated natural destruction and a little sword-and-sandal action thrown in for good measure. On top of all that, there's the deep resonance of reality, the utter destruction of a prosperous Roman city, whose population died beneath layers of molten ash. But then we see the director's name over the credits: Paul WS Anderson. He of Alien Vs Predator fame, a Death Race remake with Jason Statham and, most ignominiously, the dire Resident Evil series of futuristic action adventures. And we prepare for a little less.

Pompeii does indeed fall short of its promise. At the same time, it offers some pure, enjoyable cinematic escapism and, in terms of sheer spectacle, is impressive.

It opens with a brief and bloody prologue set in Britain in AD 62 as a Roman army led by Corvus (Kiefer Sutherland) slaughters an entire tribe, with only a boy, Milo, surviving. Fast forward 15 years to Londinium, where Milo now takes the strapping form of Kit Harington, aka Jon Snow of Game Of Thrones fame, equipped with his trademark locks from the TV series and the exaggerated, de rigueur abs of film fantasies such as 300. The young slave has become a skilled gladiator; a slave owner is persuaded that Milo is "wasted out here in the provinces" and transports him to Pompeii.

Here, the young Briton falls in love with a sympathetic Pompeian, Cassia (Emily Browning), whose wealthy parents (Jared Harris, Carrie-Anne Moss) are attempting to lure Roman money to help their development of the city. Unfortunately that investment comes courtesy of a certain Corvus, now a senator, who has decided that he wants Cassia as his wife. With the festival of Vulcanalia in full swing, Milo and new gladiator friend Atticus (Adewale Akinnuoye-Agbaje) prepare for the games. And the nearby Vesuvius starts clearing its throat.

Plot and character-wise, it's very much like a Roman road - reliable but straight, with nothing much by way of original deviation. All the echoes of other films - and there are many - simply remind us how better those films were. As a disgruntled gladiator, Harington is a sullen boy compared to Kirk Douglas's Spartacus or Russell Crowe's Maximus; Sutherland's ill-advised voice, clipped with traces of wispy camp, makes one pine for Laurence Olivier's patrician baddie, also from Spartacus.

More important than making such distinctions, is to wonder why one's making them in the first place. Surely the appeal and the challenge of the story of Pompeii would have been in capturing the society that was so abruptly wiped out - its different social levels, the life on the streets, in the bath houses and the villas, giving a complete, devastating sense of what was lost. This approach used to be the bread and butter of disaster movies such as Earthquake and The Poseidon Adventure, offering a societal cross-section, an ensemble whose gradual demise had cumulative effect.

But Anderson doesn't attempt this at all. Making Pompeii rest on a rote rebel-slave tale is dreadfully limiting, and opening the film with an excerpt from Pliny the Younger's actual eye-witness account of the catastrophe is a shot-in-the-foot reminder of the opportunity lost.

To his credit, the director does orchestrate some very exciting gladiatorial fights, especially one pitching Milo and Atticus against a small army of opponents, and the eruption is spectacular - including the collapse of the coliseum, fireballs and a tidal wave that sends ships cascading down the city streets. Akinnuoye-Agbaje makes a noble sidekick, Harington and Browning comely leads.