The film-it-yourself YouTube generation has inspired its first monster movie in “Cloverfield,” a short, intense, and scary flick that plays out the way “Godzilla” would have if it had been shot with a bystander’s camcorder.

That is the central conceit of the film, which was produced by J.J. Abrams (mastermind of TV’s “Lost”), written by frequent collaborator Drew Goddard, and directed by Matt Reeves. Someone is videotaping the events at a going-away party for a friend when a giant something-or-other attacks the city. We see only what the video camera sees, the footage apparently having been discovered by rescuers or clean-up crews after the fact.

Call it a gimmick if you must, but it works. Since we only know what the camera-wielder and his friends know, we’re as terrified and nervous as they are. The scenario calls for naturalistic, improvised-sounding dialogue, too, which is rendered with complete authenticity by the small group of mostly unknown actors. In short, there is very little about the film to suggest it’s not exactly what it claims to be. If it weren’t for the dearth of news reports about New York City being attacked by a giant monster, you’d accept the film as a documentary.

The footage comes from a night in May when a group of twentysomethings are celebrating their friend Rob (Michael Stahl-David) and his new job in Japan. Rob’s brother Jason (Mike Vogel) has thrown the party and put their comic-relief pal Hud (T.J. Miller) in charge of getting video testimonials from everyone. Jason’s girlfriend Lily (Jessica Lucas) is there; so is a girl named Marlena (Lizzy Caplan) whom Hud has a crush on — and so is Beth (Odette Yustman), Rob’s long-time friend and one-time hookup who has shown up at the party with another guy.

With those basic relationships established, we get to the heart of things when explosions and fires suddenly rock lower Manhattan. Through Hud’s camera we see panic in the streets as buildings collapse and the Statue of Liberty’s head comes soaring in from the harbor. Hud continues to film as much as he can, realizing immediately that people will want a document of this.

It is impossible to see amateur footage of crumbling buildings and fleeing New Yorkers without thinking of 9/11, and that connection is eerily (perhaps insensitively) established further when survivors begin walking across the Brooklyn Bridge. I’m tempted to read some deeper subtext into the filmmakers’ invoking of those images — something about how the monster represents all our fears, real or imagined — but I don’t think there’s really anything more to the film than what’s on the surface.

In a way, Hud’s position as cameraman makes him the central character, though of course it also means we almost never see his face. The real protagonist is Rob, who argued and parted with Beth before the mayhem began and must now rescue her before the military locks down the city. Snippets of what was on the tape before Hud started recording over it show us Rob and Beth’s prior relationship — a truly ingenious storytelling device — and we feel for them about as much as we ever feel for anyone in these kinds of movies.

Characterization is not the film’s strong suit, but neither is it the point. I’m actually surprised that we get as much as we do, given the restrictions of the format: no flashbacks, no internal monologues, no tender, well-lit close-ups. It’s also very intriguing to see the same types of characters and situations as these movies usually have, only from a you-are-there point of view.

“Cloverfield’s” mission is to thrill us with creature-induced pandemonium, and it does that better than any American monster movie in years. We feel like we’re there with Rob and his friends, susceptible to the same surprises and horrors, and trapped by the same limitations. And since the characters are just regular kids, not heroes or military personnel, we instinctively understand that the movie will not end with Rob firing the shot that kills the monster and then being given a medal by the president. It will end with Rob escaping the monster, or with Rob being killed by the monster. Those are the only realistic possibilities.

With that grim knowledge in mind, prepare yourself for a uniquely well-executed and unnervingly fun creature feature. Here’s hoping the new season of “Lost” is even half as satisfying.

A- (1 hr., 24 min.; PG-13, some profanity, lots of scariness and tension, brief strong violence.)