WE FIRST heard of Cloverfield last summer when a deliberately perplexing trailer - lots of screaming and panicking in New York - appeared before screenings of Transformers.

Noting the involvement of arch trickster JJ Abrams, the creator of Lost, cynical observers suggested that, whatever the film might concern, it would, surely, have nothing to do with the destruction of Manhattan by something big and scaly. That would just be too obvious.

Well, it seems as if Abrams, credited here as producer, has pulled a cunning double-bluff on us. This unusually exciting, disconcertingly brief shocker does indeed detail the advance of an enormous lizard through American cinema's most annihilated burgh (how come these beasts never end up in, say, Hull or Lahinch?). But the film is really about two millennial dogs that, to this point, have stubbornly refused to bark at the movies.

We should, perhaps, not be astonished that cinematic allusions to the attacks of 9/11 have, to this point, been obtuse - an allegory here, a hint of paranoia there - and largely confined to big, serious films about big, serious people. More surprising is the negligible influence of 1999's Blair Witch Project on mainstream movies. Wasn't the domestic camcorder supposed to have eaten the industry alive by now?

Cloverfield, directed by Matt Reeves, a TV veteran, begins with a message explaining that the videotape we are watching was found in the area of New York "formerly known as Central Park". We then spend some time with dishy Rob (Michael Stahl- David) and sleek Beth (Odette Yustman) as, frolicking about a still intact city, they appear to lay the foundations for a romance.

Suddenly, the picture cuts to a party. It transpires that Hud (TJ Miller), in documenting a going- away do for Rob, has taped over a treasured record of a brief, idyllic fling. As the movie progresses, snippets of that romance offer poignant counterpoints to the accumulating mayhem.

The film stays with the self-absorbed partygoers just long enough for us to pray that something massive might emerge from the Hudson River and bite their fluffy heads off. Suddenly, a massive explosion interrupts their vapid conversation and the Statue of Liberty's head bounces down the street. There is inhuman roaring as well.

Cloverfield, even more than Blair Witch, asks us to accept that people might, under the most absurdly stressful situations, continue to film the destruction around them: Hud witnesses the collapse of bridges, helicopter crashes and underground attack by spiny things, but never drops the camera.

If, however, you are prepared to allow that absurdity and you have a resistance to motion sickness, then you should have a whale of a time. The pseudo- subjective camera bestows a terrifying immediacy on the action, and Reeves does a terrific job of showing just enough of the creature to tantalise.

One might question the ethics of composing a shot directly modelled on news footage of 9/11 - debris drifts down an avenue while policemen and soldiers attempt to order the crowd - but it cannot be denied that the association adds a chilling frisson to the action.

More than anything else, Cloverfield is to be praised for allowing a welcome degree of vagueness into proceedings. As viewers of Lost will attest, JJ Abrams is the master of the unanswered question. In that series, the galloping quandaries became frustrating, but, at just 85 minutes, this less fussy thriller never even threatens to offer solutions to its intriguing riddles. The pondering is part of the fun.

Where did this big stompy thing come from? What are those smaller creatures spilling out of its sides? What's going on in the tent? Exactly what did happen to the directors of The Blair Witch Project?