The relaunch of Scooby-Doo, a character born in the late 60s and sustaining a presence in the decades ever since, carries with it the potential for both high highs and low lows. Because universal familiarity and affection among parents might make it a swifter rental decision but the weight of expectation and of childhood association will mean that casual, uninvested background watching won’t suffice. Which is where the problem with Warner’s early summer franchise-relauncher Scoob lies. While a younger audience might be enthralled by the fast pace and bright colour palette, those understandably curious adults sitting nearby will find themselves watching in horror, a deep, sorrowful howl emerging.

Originally intended for a theatrical release, the studio decided to demote their animated adventure (the first big-budget Scooby-Doo film since 2004) to the home cinema, a wise sacrifice given a captive family audience thirsty for new content as shown by the controversial success of last month’s Trolls: World Tour. Scoob has a steeper hill to climb though, without the inbuilt younger fandom of Universal’s sequel, so it’s important to woo an older crowd and so while longtime animation director Tony Cervone might be at the helm, the script includes input by comedy writer Adam Sztykiel, whose previous projects have been aimed at adult viewers. The end result, trying to appeal to both ends of the spectrum, can’t quite master something that say, Pixar, manages with ease. It’s uncomfortably strained with laboured winks scattered among the sub-par slapstick action, a dog’s dinner of a movie best enjoyed by those with no knowledge of who or what Scooby-Doo used to be.

But even then, Scoob stumbles because so much of the plot plays off an assumed knowledge of the history of these characters and their dynamic, hoping that we fill in the many gaps it can’t fill itself. It starts promisingly, with a neat meet-cute as we learn how a young Shaggy befriends a stray dog he calls Scooby-Doo. On one Halloween night, the pair then end up meeting three friends, Fred, Daphne and Velma, who help them bring a thieving local in a ghost mask to justice. It’s a charming throwback and so it’s then frustrating that we’re dragged into the future via lazy mystery-solving montage as the gang find their business underfunded leading to a bizarre and dated cameo from Simon Cowell, playing himself as a potential investor. He bitchily recommends dropping Shaggy and Scooby from the Mystery Inc banner and so the group splits, a befuddling inciting incident that’s indicative of a confused and confusing plot to come.

The ensuing mess of events continues to take us further away from the ingredients that made the original show and its many iterations so well-loved by so many, replacing a goofy small-town mystery with a blockbuster-level global quest. In trying to update the formula, the film’s four writers have expanded the focus too wide, flattening out the distinctively shaggy mystery elements and turning it into just another soulless kids movie. The tiresome insertion of a superhero narrative feels patronising, as if a younger audience can’t be trusted without it, and transforming kitschy Wacky Races bad guy Dick Dastardly into a slick, all-powerful supervillain is both boring and a predictable sign that a Hanna-Barbera cinematic universe is upon us.

There’s something too big about the plot, making it feel more like the third or fourth instalment in a franchise, rather than the more modest scene-setter it needed to be. We get so little time with the group as a whole and have such little understanding of what it is they actually do that suddenly throwing them into jeopardy doesn’t have much of an effect, especially when it’s on such a large scale. It doesn’t help that the garish animation looks more suited to a mobile game than a studio movie, passable in the bigger action sequences but hideous when trying to portray human features. There’s a stacked voice cast – including Zac Efron, Mark Wahlberg, Gina Rodriguez and Amanda Seyfried – and while Will Forte nails his Shaggy impression, the others are hard to distinguish, struggling to add life to a script that relies on clunky pop culture references (most of which conveniently nod to other Warner properties).

At one point in Scoob, Fred insists that this is their “most important mystery ever” rather than being “about some guy in a rubber mask”, an annoyingly smug attempt to elevate this above the many entertainingly dopey adventures we’ve seen them on before. But the bigger Scoob goes, the more anonymous it feels, a lacklustre example of what happens when Hollywood execs pander, meddling with a classic that should have been treated with more respect.

• Scoob is now available digitally