In this follow-up to 2009’s Avatar, when the humans come back to Pandora, Jake Sully (Sam Worthington) takes his family on a three-plus hour retreat to the Metkayina clan of ocean-going Na’vi, in what is on track to become this year’s most urinated-during film.

Director James Cameron spent the best part of a decade developing the underwater motion capture technology needed to film Avatar 2. If only he’d spent more than a day working on the script. Jake, Neytiri (Zoe Saldana) and family have the likeability of the circuit boards they were built on and the relatability of the great barrier reef. The premise feels ripe for fish-out-of-water humour but this Na’vi-in-water movie is a family comedy without the comedy.

Say what you like about the story, characters, acting and dialogue, it deserves an Oscar for project management. There are some incredible sea-quences here, so every time you start to break into laughter about how pathetically bad it is, something shiny forces its way in to your brain and you marvel at the sheer logistics of producing something so technically demanding.

The visuals are jawdropping. Cameron – who also holds the record for deep sea diving – is surely one of the best-qualified people in the world to create realistic water effects, which are almost like watching a video of some real water. The CGI has a remarkable physicality to it, and often looks completely real. The 3D effects have also greatly improved. Not since The Marriage of Figaro has such technical virtuosity been paired with such a farce.

It is the first film I have ever wished I watched on a smaller screen. The experience of watching it on a giant IMAX screen is like standing 25m away from a major fireworks display for over three hours. It will be etched onto your retinas and ringing in your ears when you lie down in bed whether you like it or not.

It’s also highly political, with Cameron coming down firmly on one side of the “white people with dreadlocks” debate. He does well to keep the ecological message at its core – a graphic and prolonged space-whale-hunting sequence will surely reach people who would never watch a film about actual space whale hunting. But this message may get lost if your brain has already seeped out of your eyes. Was it worth 13 years, Kate Winslet holding her breath for seven minutes and enough computing power to put a person on Mars? I bloody H2Ope so.