On the surface, this looks like ludicrous sci-fi fun. But Matt Reeves's monster movie is a good deal better than that, using the simple expedient of hand-held camerawork throughout and showing us only what its human characters would see as they flee the strange creatures who threaten Manhattan.

It isn't always an easy watch for those who find shaky, off-kilter photography too much to take. But the idea behind the film - that, were its audience in the same predicament as the characters, we would be as confused and terrified as them - comes over better and better as the tall tale progresses.

There is not a very auspicious beginning. We see two lovers (Michael Stahl-David and Odette Yustman) using a camcorder to detail their burgeoning romance. Later, a friend (TJ Miller) is assigned the task of recording on the same machine the young man's party, organised before he leaves for Japan.

This lasts for some 20 minutes and since none of the party people, let alone the lovers, seems more than marginally intriguing, you begin to wonder what on earth the film is going to be about.

Then comes the bombshell. The lights go out, the building shakes and the group begins to think an earthquake is on its way.

In the dark streets buildings topple, the head of the Statue of Liberty falls at the screaming party-goers' feet, looters grab what they can from devastated shops and a vague outline of the monster appears overhead.

We never see it clearly, though it seems to be spewing out small, crab-like creatures as troops move in and aircraft unsuccessfully strafe it.

It's a menace that can be glimpsed only as much as the fugitives might have managed, nervously pointing their camera into the night sky.

The friends find sanctuary first in an underground tunnel and then in a National Guard helicopter which arrives to save them. But that crashes and they are back trying to find an ever more unlikely escape route out of the city.

Not a great deal of acting is required of anybody, bar looking suitably terrified and running like mad. And there are several scenes which remind one a little too closely of 9/11 to be entirely tasteful.

But the camcorder records and we watch. It's an audaciously original roller-coaster ride which delivers even if at first it doesn't look as if it's going to.