Cinema history has been made in America. Box office takings hit a new record of $275 million over the Christmas weekend, largely because of James Cameron's Avatar. Unless you have been living in a small cave, or perhaps on Pandora, the planet where the film is set, you cannot have missed the Avatar marketing campaign. Every billboard and bus is sporting a picture of a blue fella with a yellow eye. Every newspaper has run a story on how this is the film which will finally revolutionise 3D cinema (a full fifty-five years after The Creature from the Black Lagoon waved his webbed paw slightly nearer an audience's face than previous technology allowed). And the marketing has worked - audiences have been flocking to see Cameron's first movie since Titanic came out in 1997.

So it's a pity that Avatar absolutely sucks. It's true that the 3D stuff is awesome. For the first time, we have a 3D film doesn't have a random scene with a ping pong ball (House of Wax), a rake (Friday The 13th, Part III), or a woman having sex with a lamp (The Stewardesses), purely to show the audience how 3D it is. Avatar isn't in 3D for a gimmick, it's in 3D because it creates an immersive experience for the viewer. Pandora feels touchably real, precisely because it appears to stretch out around you, in minute detail, in every direction.

But that's where the good stuff ends. Avatar is, in essence, a children's film, dragged out over 161 minutes. The plot is risibly thin: evil earthlings (Americans, obviously. Period drama has evil Brits, present day drama has evil Arabs, but in the future, Americans are the villains) are trying to destroy the woodland habitat of the nature-loving, tree-hugging Na'vi. Keen sci-fi viewers should know that any time a race of aliens has an apostrophe in their name is a time to worry. It's as though the apostrophe stands in, not for a missing letter, but for story, character and fun.

But why, you might wonder, would evil earthlings be destroying the forest of the tall blue aliens? They are mining for a rare mineral, obviously. But how rare could it be? Surely they could try to find it somewhere else, and leave the trees alone? No, they could not. And we know that, because James Cameron, in a screen-writing moment which must surely have been the consequence of a lost bet, named the mineral Unobtainium. Yes, you read that right. Unobtainium. So we can probably assume it's pretty hard to find.

This could have been a great sci-fi film about resource scarcity, immigration and integration. It didn't have to be dull, either: look at District 9, which dealt with precisely those issues this year and never lost its humour, pathos or kick-ass fights. But Avatar is a worthy eco-drama which occupies the seemingly unfillable space between Last of the Mohicans and Disney's Adventures of the Gummi Bears. If you need a blue fix, read the Smurfs.