Warning: This review contains a minor spoiler. As in relatively unimportant, not a plot point concerning a child.

You could say there’s a loose, freewheeling quality to Thor: Ragnarok and you’d be right, because there is. Director Taika Waititi allowed his cast to improvise bigly, and whereas this is usually the death knell for a movie, particularly one with comic pretensions (see any collaboration featuring James Franco, the palsy inducing remake of Ghostbusters), here it manages to avoid being intrusive, let alone ruinous. Perhaps that’s because so many of the beats in any Marvel movie are set in stone long before production rolls, appointing a director is just a proxy for calibrating tone. The picture’s going to be stuffed with rendered worlds and setpiece action, making dialogue almost superfluous. Well, if it’s going to be incidental, why not treat it as such? Why not just let the cast make it up?

One reason would be that such an approach might rob the movie of any dramatic heft. This presupposes this was a priority of course, but nothing in Ragnarok has any weight. It’s a film built on the kind of exchanges you used to see in Mel Brooks genre spoofs. “We’re coming up on the Devil’s Anus” is an actual line of dialogue in what professes to be a real franchise movie. Acknowledging the inherent ridiculousness of it all makes for enjoyable viewing of course, but where, Chris Hemsworth’s musculature aside, is the beef?

All this begs the question, if the filmmakers aren’t taking the plot seriously, why should we? It matters less when the situation is frivolous, namely Thor forced to engage in gladiatorial combat with old pal The Hulk, or Jeff Goldblum’s Grandmaster shooting the shit on his fiefdom in trademark staccato style. But because this is likely to be Thor’s final solo outing, there’s a job of character development to be done here – the death of Odin, The God of Thunder embracing his true power and destiny, etc – and it’s hard to sell those wrap up moments as significant in a movie that cuts between plot advancing villainy on Asgard, spearheaded by a scene chewing Cate Blanchett, and jovial knockabout fun with Thor, Loki and the gang, without changing gear.

Ragnarok’s improvised dialogue is fine, though largely meandering and witless (the mark of the beast); it’s an approach designed to induce a warm glow complementing the movie’s colourful production design and Mark Mothersbaugh’s retro-inspired disco score. But it characterises a movie that’s a little too long and a little light to be anything other than pleasingly disposable. Yes, it’s a starter ahead of next summer’s Avengers: Infinity War blowout – something to line the stomach, but Marvel shouldn’t forget that a guaranteed audience and a multi-film arc doesn’t absolve them from their obligation to make each episode a satisfying (and memorable) film in its own right.