The Lego Ninjago Movie is more than a few bricks short of a full load.

The latest entry in the Lego feature film franchise is also its most blatantly cynical toy commercial, offering little in return for your forked over ticket money other than a needlessly starry cast, a weak storyline and a massive middle finger to fans of the original “Lego Ninjago” cartoon series.

When evil Lord Garmadon (Justin Theroux) launches yet another attack on the island of Ninjago, it’s up to the Ninjas to repel him once again. Unbeknownst to Lord Garmadon, the Green Ninja (Dave Franco) is his estranged son Lloyd and when Garmadon gains the upper hand in the final battle for Ninjago, Lloyd disobeys his sensei and uses the ultimate weapon, drawing the monster Meowthra down on the island. To save the day, the Ninjas must journey to a hidden castle in search of the ultimate, ultimate weapon.

The original TV series on which the movie loosely draws from (itself based on an existing Lego toy line) tells the story of Master Wu, who sets out to train elemental ninjas in the art of Spinjitsu, battling Garmadon, his master The Overlord and their army of snake men. It offers a witty and wryly wise action comedy adventure with surprisingly strong character development over the course of its (so far) eight seasons.

The movie version jettisons nearly all of this mythology and the original voice cast in favour of a celebrity-voiced generic martial arts adventure that plays out like a Mega Bloks “Power Rangers” knock-off rather than the prestige Lego movies we’ve come to expect. The changes might not be so aggravating were they not so comprehensively and surgically aimed at selling merchandise.

You’ve bought your tickets and been provided with a flaccid and uninspired script which exists merely to pad out the running time and join the good bits they showed you in the trailer, so why not pick up the video game? Maybe you’re coveting the prominently featured Green Ninja Mechadragon? Or the Fire Ninja Mecha? Or maybe the Mecha Man Garmadon builds once he sees the other ninja have them? Hell, why not just go all out and splurge £109 on the Master Wu’s sailing junk Destiny’s Bounty model where several key scenes are set? At the very least buy a lunchbox, yeah?

Younger fans of the TV show may find the voice cast changes and complete discontinuity from their favourite TV show disappointing or unsettling. Even the personalities of the characters have changed without good reason and the brief nod to the TV series when Lloyd’s ringtone is revealed to be the theme tune just rubs salt into the wound. If any of these changes resulted in a better movie, they could easily be overlooked but they don’t. “The Lego Ninjago Movie” tries desperately to mimic “The Lego Movie” and “The Lego Batman Movie” but it has less than a tenth of the wit of the former and none of the energy and brio of the latter. It’s incredible to think this dreary brickfest was overseen by Phil Lord and Chris Miller themselves although suddenly, I can see Kathleen Kennedy’s point of view. Do yourself a favour: binge watch some of the TV show and wait for this cynical cash grab to turn up on Netflix.