There are decent performances from Cynthia Erivo and Ariana Grande – but this flat opening episode of The Wizard of Oz prequel may not convert those who aren’t already superfans.

One of the most important things to know about Wicked, the big-screen adaptation of the hit Broadway musical, is that it’s not actually a film adaptation of the hit Broadway musical: it’s an adaptation of the first half. The title, both on-screen and off-posters, is Wicked Part One, and ends with the caption “To Be Continued”, so viewers should be warned. We’ve had similar tricks played on us by the creators of Mission: Impossible – dead reckoningand Harry Potter and the Deathly Hallows, but it’s still frustrating to realize that after two and a half hours you’re only halfway through the plot and that Part Two won’t hit theaters for another year. It’s like being kicked out of a theater during intermission.

Whatever the filmmakers’ reasons, you can’t help but resent their arrogance. The implication is that their story is so profound that it requires a full five hours of screen time. And Wicked won’t convince everyone that that’s the case.

For those who haven’t seen the show, which premiered on Broadway in 2003 and has been running ever since, it is a spin-off of L Frank Baum’s The Wonderful Wizard of Oz, which follows the backstory of Glinda the Good and the Wicked Witch of the West. It begins near the end of the classic 1939 film, The Wizard of Ozwhere the evil witch is dissolved by water that Dorothy splashed on her. Glinda visits the Munchkin village to share the happy news, whereupon the Munchkins ask her about the friendship she had with the Wicked Witch in days gone by, when her name was Galinda. And so begins a story that can best be described as Harry Potter meets Mean girls. Set largely within the Italianate walls of Oz’s obnoxiously named Shiz University, it charts the relationship between the attacked Elphaba, played by Cynthia Erivo, and the confident Galinda, played by Ariana Grande-Butera (i.e. the pop star known as Ariana Grande, but her full name is shown on screen).

Elphaba was born with pea green skin, which has always made her feel like an outsider. Her telekinetic powers, which come to life when she’s angry, don’t help matters either. And actually, she only came to Shiz University to keep an eye on her sister (Marissa Bode), who uses a wheelchair. Galinda, meanwhile, is the archetypal American queen bee, a clothes-obsessed blonde who is adored by everyone around her almost as much as she is. These two resent each other once they’re forced to share a room — they even sing a duet on the subject — and the situation is made worse when the university’s magic teacher, Madame Morrible (Michelle Yeoh, who’s not a singer) prefers gives to Elphaba, and the handsome Prince Fiyero (a scene-stealing, swaggering Jonathan Bailey) prefers Galinda. Or is it?

If you’re already a fan of the musical, you’ll probably appreciate the meticulous work that director John M Chu (Crazy rich Asians, In the Heights) has done to bring it to the silver screen. There’s a slick screenplay to it Winnie Holzman and Dana Fox, Stephen Schwartz’s songs are grand and stirring, and you can tell that armies of artisans worked for days on every wig, embroidered jacket and decoration on the colorful, shiny man-made backdrop. The two leads are also well cast. Erivo is disarmingly sweet and vulnerable, but retains a hint of latent menace, and Grande-Butera, who can hit notes so high that only dogs can hear them, is funny as a cheerfully perky narcissist. She would have been interesting Barbie if Margot Robbie hadn’t played the role.

However, if you’re not already a fan of the musical, you may not be converted. The film ends with a song called Defying Gravity, so it’s only fair to say that’s exactly what Wicked fails to achieve. It doesn’t take off. It doesn’t have the great jokes, the surprising twists, or the stunning dance routines that might have enchanted you, and it’s weighed down by underdeveloped subplots and underutilized supporting characters (who presumably have their moment in part two). ), but also by his own sense of self-interest. With every blood-curdling empowerment song, Wicked seems to declare that it is an important work of art. And yet the message about not mistreating people just because they have green skin isn’t exactly subtle, and the questions the film answers aren’t exactly urgent. Why does Elphaba wear a pointy hat? Why did Galinda change her name to Glinda? How can the flying monkeys fly? Why is the yellow brick road yellow? These aren’t the most crucial issues in the world, but if you’d like to see a Wizard of Oz prequel, I’d recommend Sam Raimi’s Oz the Great and Powerful, which came out in 2013.

Wicked is drawn out and boring in comparison. It might have been lighter if the editors had created a subplot about magical talking animals, which adds nothing except a few minutes of running time. And they could have cut off Elphaba’s sister, who has astonishingly little to do. That way, the film could have condensed the entire musical into one fast-moving, satisfying entertainment. As it is, I strongly suspect that Wicked will work much better as the first part of a double bill, with Wicked Part 2 shown after an intermission. But to know for sure we will have to wait another year.

Wicked is released in UK and US cinemas on November 22