The latest in the sci-fi adventure series is the longest and worst yet

The third instalment in James Cameron’s mega-hit blockbuster franchise is “197 minutes of screensaver graphics, clunky dialogue, baggy plotting and hippy-dippy new-age spirituality”.

Avatar and Avatar: The Way of Water are two of the highest-grossing films ever made, so you can hardly blame James Cameron for keeping his sci-fi adventure series going. But its third episode, Avatar: Fire and Ash, strongly suggests that he should quit while he’s still ahead. Each Avatar so far has been longer and worse than the one before, and this one – a full half-hour longer than the 2009 original – is 197 minutes of screensaver graphics, clunky dialogue, baggy plotting and hippy-dippy new-age spirituality. It’s terrifying to think that Cameron still has two more sequels scheduled. How much longer and more self-indulgent can they possibly get?

The most insulting part is that even with that preposterous, bladder-testing running time, Avatar: Fire and Ash doesn’t work as a standalone film with a beginning, middle and end. Making no concessions to any viewers who aren’t superfans of the franchise, Cameron assumes that we’re already deeply invested in the characters, their relationships and their surroundings, so that a complete, propulsive story is surplus to requirements.

It feels as if we’re a zillion light years from the excitement of the first film. The idea of that one was that the human race had made such a mess of the planet Earth that they decided to exploit the mineral resources of an Edenic, unspoilt moon named Pandora. This plan wasn’t popular with Pandora’s blue-skinned humanoid inhabitants, the Na’vi, but a human Marine, Jake Sully (Sam Worthington) had his mind zapped into the body of a Na’vi-human hybrid, so that he could cosy up to the locals. He then fell in love with a Na’vi princess, Neytiri (Zoe Saldaña), and fought alongside her tribespeople against the invaders from Earth. In short, Avatar was Pocahontas meets the Smurfs in space – a scenario ripe with conflicts and environmental issues.

The situation now is that the Na’vi are still fighting against the human military, but it seems that Cameron has lost interest in Jake and Neytiri, and now prefers to hang out with their teenage children. It’s a fatal mistake. Worthington may not be the world’s most charismatic actor, but at least his character was distinctive, whereas it’s sometimes hard to tell which of Jake and Neytiri’s nearly-naked offspring is which – and they’re all equally annoying. Every now and then there will be a big battle, or we’ll see some human scientists who haven’t been in the film for ages. Sometimes we’ll have to sit through long, reverential discussions of the Na’vi’s beliefs. And sometimes we’ll have tantalising glimpses of the hard-edged empire-vs-rebels eco-thriller that the film could have been. But, essentially, Avatar: Fire and Ash is a Californian soap opera in which various forgettable dreadlocked surf dudes ride dragons and shout phrases like, “That was insane, bro,” and, “This is sick, cuz!”