So despite a predictable childhood obsession with James Cameron’s Aliens and Terminator 2, I approached Avatar with a healthy dose of skepticism. With its maybe $300 million budget – and the swirling rumours of much, much more – I was afraid that no matter how good a film it might be, I’d be stuck staring at the price tag dangling invisibly from the corner of the screen and wondering if it was worth it.

But Avatar successfully stopped me thinking about its dollar signs. It’s a massive 160 minutes long and I didn’t once look at my watch. Yes, it trades in clichés – ‘naive scientists’, ‘evil corporations’, ‘noble savages at one with nature’, and (perhaps unfortunately) ‘white man saves the day’. Some are already complaining that the story’s too simple. Well, ‘complicated’ doesn’t equal ‘good’ – Matrix sequels anyone? – and Cameron’s simple story is masterfully told.

It’s far too deliberately paced for action fans, and barely a sci-fi at all. Cameron has little interest in exploring any ideas behind the projecting-human-minds-into-alien-bodies technology that provides the film’s title. It’s a deeply earnest and old-fashioned adventure story. If anything, Avatar is a conceptual, mirror-world sequel to his Aliens from 1986. Imagine if one of Aliens’ marines had a change of heart and decided to fight alongside the creatures with acid for blood. It even has a new Paul Reiseresque corporate stooge!

And here’s the ultimate compliment for Avatar’s special effects: they’re so good that I don’t feel much of a need to talk about them. Yes, the world of Pandora and its giant blue inhabitants is visually overwhelming at first. Too busy, too day-glow, too outdoor rave. Once you adjust, Avatar is completely immersive. The Uncanny Valley that turned films like The Polar Express into horrific parades of undead fleshbots is nowhere to be seen – thanks to being artfully subsumed into alien facial features.

I’m nervous about saying it in case Avatar completely falls apart on a second viewing, but there were brief flashes where I felt like a kid watching Star Wars for the first time.

All Avatar‘s above pleasures, however, depend on your ability to process this pair of facts: it’s about a noble indigenous population fighting corporate greed and American imperialism in defence of their world’s vibrant ecosystem… that also happens to be the most expensive film ever made.

As Alanis Morisette might say: that’s the black fly in your chardonnay.

Does the production of a film affect your enjoyment of it? Read this unmissable New Yorker piece about Cameron’s creative process on the set of Avatar, and wonder if we should dismiss all art made with money that could have been better spent. I think it’s only human to hear an obscene Hollywood budget like this and have a flicker of thought about starving third world children – but if you follow this logical path, it becomes increasingly difficult to justify the cost of any art at all.

Is the disjunction between Avatar’s moral message and its decadent production an unforgiveable hypocrisy? Or is the fact that Cameron convinced his backers to throw hundreds of millions at a film that’s so overtly anti-corporate and anti-America the ultimate act of insider subversion? Does it matter?

If it sounds like I’m making excuses, I don’t mean to be. It’s perfectly reasonable to think the amount of money spent of Avatar is repulsive, and avoid it for that reason alone. It’s to James Cameron’s credit, though, that I was so completely taken in by the movie that these questions didn’t even occur to me until after the credited rolled – and after the hideous Titanic-style ballad began.

(Admittedly, I’ve been a fan of McG since the first Charlie’s Angels, which combined the shimmering, high-energy fun of an old Hollywood musical with a sword-fighting Crispin Glover.)

Others have written in detail about what went wrong with the movie: how John Connor’s scenes were reportedly added piecemeal to the screenplay, explaining why they feel so redundant and barely half-stitched into the fabric of the film. HowTerminator Salvation fails most spectacularly, though, is as a satisfying sequel.

A good sequel is a complicated tightrope-walk between repetition and variation, and back in 1991 Terminator 2 struck the ideal balance. It took familiar elements and twisted them, so we saw Sarah Connor transform from lonely waitress to pre-apocalyptic warrior; saw the unstoppable high-tech terror of the first film become the desperate underdog when pitted against liquid metal; and saw the superb bad-Terminator-becomes-good-Terminator fake-out (which, yeah, everyone knew in advance, but still).

Now John Connor’s been told he’ll be the Saviour of the World from long before he did anything to justify it, and pop-psychology dictates that’d screw you up into a fascinating wad of dramatic issues. He should be inspiring fascinating madman-or-messiah reactions everywhere he goes. In Terminator Salvation, it’s like the screenwriters were told not to mention the earlier films in any detail – with no time travel talk, especially. John Connor knows that he has to save the young Kyle Reese in order to later send him back in time to become John’s father. We know it too. But for some reason it can’t be said out loud, leaving John shouting about how “the future’s at stake!” without anyone reacting beyond a kind of “Oh, that John…”.

Instead, Terminator Salvation trades on the surface affectations of its sequel status, like Linda Hamilton returning to record some pointless Sarah Connor voiceover tapes, or the much-discussed digital Schwarzenegger cameo, or John Conner saying “I’ll be back” – with an appropriate didja-catch-that-huh? music cue.

Sure, James Cameron used all these tricks too, but he balanced it with masterful high-concept storytelling techniques. His dialogue might occasionally exhibit a blistering case of the George Lucases, but in Terminator 2 his sequel-logic is note-perfect.

One last thing: there’s another pitfall inherent in going back to the same stories again and again, and it’s the reverse of the old ‘show don’t tell’ that’s inevitably bandied around during the first week of any creative writing class. The problem is that some things are much more powerful when they’re just imagined than when they’re actually splashed up on the screen for all to see.

Is the looming apocalyptic robot-war more interesting as a terrifying hypothetical? Reese explaining the future is much more harrowing than any of the flashbacks to the future in the first Terminator. (Okay, okay, except for the iconic scenes of a tank-tread rolling over human skulls, which haunted my misspent, violent-movie-watching youth.)

The first film’s final moments of an approaching storm hold much more menace that the grim reality of Salvation: