There's one thing that must be of inexorable comfort to James Cameron in the wake of the mixed response to both the Avatar trailer and the fifteen minutes of footage revealed on 'Avatar Day' last Friday: prophets of doom have written him off before. Most notably before he broke pretty much every box office record on the planet with Titanic in the late 1990s.

Cameron is one of a handful of people in Hollywood who are truly given their head as regards new projects, and the fact that the portentous rumblings of box-office doom turned into phenomenal returns for Titanic must have Cameron's latest investors crying 'hold' on the not-entirely-rapturous response to the Avatar peeks.

Cameron ushered in a whole new era of unhappy endings in movies with Titanic; influenced the look of the first-person shooter forever with Aliens; spearheaded the true CGI revolution with the ground-breaking effects in The Abyss and Terminator 2: Judgment Day. Cameron delivers. And Hollywood needs him to now, most especially because if Avatar can repeat the success of Titanic, the movie execs win a huge battle in the fight against piracy, and in the struggle to re-sell their catalogues yet again on Blu-ray....

Avatar not only has the potential to become Blu-ray's Matrix - i.e. the product so essential to a new technology that it popularises it, as The Matrix did for DVD - but to disseminate 3D technology as the cinematic consumer experience that can neither be pirated nor downloaded, but must be paid for legitimately in movie theatres.

Hollywood liked it back when movies were (as John Hammond observes in Jurassic Park) 'a bit of a ride', rather than a customisable and consumer-friendly experience; both the relative rigidity of Blu-ray and the 'pro' culture of cinematic 3D have the potential to deliver this again.

So perhaps it doesn't matter that most of the CGI in Avatar seems to be operating at a pre-Lord Of The Rings level; that James Cameron is once again trying to write a convincing love-story in the face of his almost-pathologically juvenile approach to romantic dialogue; or that he seems to have pre-sold an outright fantasy movie as a sci-fi flick (an apparent fact which we have four months to get used to).

Some of the most successful romantic fiction in the world is badly-written guff with predictable characters of little complexity. I don't consider that either the Kate Winslet or Leonardo Di Caprio characters in Titanic had any significant depth, and yet I have to admit that it didn't stop their love-story becoming cinema's most popular romance since Gone With The Wind.

Likewise was Cameron able to string out a very clichéd 'cat-and-dog'-style pair of sparring lovers in The Abyss, and get away with it - that film not only didn't necessarily need the love story, it arguably didn't need the aliens.

But a Cameron movie is a buffet, and there's always something substantial left to enjoy when you have turned your nose up at the spinach canapés. Perhaps Avatar's story is so good that you will forgive Sam Worthington's head-deskingly dumb bravado, just as you forgave Leo Di Caprio for suddenly knowing all about the aquatic dynamics of sinking ships at the climax of Titanic, despite being a waster art-student.

Already I am intrigued by the Sigourney Weaver character that appeared in the earlier scenes of the Avatar previews, and keen to see more of the familiar Cameron 'real-tech' that we have already glimpsed.

It's just that I feel I shall have to sit through an interstitial ninety minutes of Last Of The Mohicans Meets Hiawatha in Pellucidar  in order to get to the bits of the buffet that I want. And usually, in a Cameron movie, these elements are a little more shuffled than they seem to be in Avatar, based on the previews so far.

I must admit, once Worthington gets into his tribal bracchiation for the admiration of Zoë Saldana, I just felt plain lost - it was as if the wrong reel had slipped into the previews. A reel, perhaps, from Pixar. Indeed, Worthington is so headstrong, even from the very second that he awakes in his avatar body, that one feels any self-serving military unit would just shoot him with a trank and ship him home in a rubber-jacket on a psych  ticket. Once 'avatared', Worthington's character is like a nine year-old boy who's determined to climb every tree, scrump every apple and learn every lesson the hard way. He makes early Skywalker look like Yoda.

It's hard to see how characterisation that raw can translate into a great movie - and yet it has, many times. At Disney and Pixar. And frankly, even they were pushing it.

What most annoys me about what I have seen is the apparent cynicism with which Cameron is trying to segue into making a completely different type of movie to any that he has made before; what's been sold at the expos and through the concept art leaks suggested some kind of hard science-fiction in the vein of his work in Aliens, The Abyss and the early Terminator movies.

Yet it seems in Avatar that all this gee-whiz science is merely there to draw the 'old crowd' in and provide some kind of rationale for a brightly-coloured fantasy-world which reflects the most emetic of the artwork plastered over teenage girls' MySpace pages. In my opinion, Avatar will prove to be Cameron's most determined grab for the young female market whose repeat-ticket sales on Titanic  turned him from a mere Big Cheese to a cardinal force in Hollywood in 1998.

Is Worthington perhaps to face off against a 'boss' villain with a grey beard who, by cybernetic implants and a unique solar conversion system, is able to channel deadly rays through his hands? A wizard by any other name...

NTTAWT. I enjoyed the Lord Of The Rings trilogy, and I'm not averse to the odd Pixar flick - I just wasn't expecting that atmosphere from Avatar; not only has the very little pre-publicity for the movie (until now) painted a different picture, but parts of the movie itself seem to be a diversionary tactic from the kind of film Cameron has really made - for the purposes of trailers and other publicity.

There are other issues: I presume there's a reason why the Na'vi, apparently an alien race, all speak English. Babel fishes, universal translators, who knows...?

I presume there's also a reason they are all bright blue (which is 'anti-camouflage' in a green forest-world, from a Darwinian point of view) and faintly resembling refugees from Cats.

I presume additionally that the elegant and apparently universal unrealistic body shape of the Na'vi will be available as a morph in Poser. The production design of Pandora seems specifically made to appeal to the sensibilities of young children in general and thirteen year-old girls in particular.

There is nothing intrinsically wrong with any of this. I just have a feeling that I have wasted a year's excitement on Lion King In Space, a prospect which would not have had my heart racing quite as much as 'the new science-fiction film from James Cameron' did.  

I stand to be corrected, awed and generally humbled, and I truly hope that I am. I also believe that a lot of fantasy fans that were only semi-interested in Avatar, but have since seen the fifteen minutes of footage, are now ravening for December 18th. And these guys (and most especially girls) are young, with money to burn - Hollywood's lodestar!

So no, I don't think Avatar will be sci-fi's Heaven's Gate, at least not in terms of box-office returns on its $180 million budget (plus development costs for the new 3D cameras). But I also find it hard to believe now that it will be a film of significant merit, particularly against the body of Cameron's previous work. Worst of all, I don't believe that it will be a 'science-fiction film' any more than Star Wars or Robots is (and actually, a lot less).

James Cameron has, I think, seen and heeded the signs of the times. If he's innovating, it seems to be only in the field of 3D movie presentation. I guess no-one ever broke even making hard sci-fi...

• Review: 15 minutes of Avatar in 3D IMAX
• James Cameron's Avatar: the trailer is here
• The Avatar Trailer: Oh dear