Sicilian location, Irish populace, Balkan Roma music: Richard Eyre’s production of a Pirandello bagatelle could easily have turned into the kind of Europudding more common in cinema. That it fairly dances over the pitfalls is due partly to a well-calibrated ensemble, but above all to the fact that the great Italian playwright made an exception to social commentary and searching examination of the human condition, coming up instead with a piece of fluff about babymaking village-style.

Over in Southwark you can currently find Rodgers and Hammerstein exploring the seamier side of life among the prostitutes and drop-outs of Pipe Dream, but in the woody amphitheatre of the Regent’s Park Open Air Theatre it’s all raindrops on roses and whiskers on kittens. Nuns, Nazis and singing children are an unlikely recipe for the most wholesome of all family musicals, but against all odds this 1950s classic is still an irrepressible hit – get out of the way or prepare to be reduced to a giddy, ecstatic wreck by a production that will send you home singing.

Rodgers and Steinbeck: sound unlikely? Well, self-proclaimed “family show” man Hammerstein may have baulked at words like "whorehouse" when he created a play for music out of Steinbeck’s Cannery Row and Sweet Thursday. But by 1955 the R&H duo had already dealt with issues like miscegenation and ageism (South Pacific), domestic violence (Carousel) and slavery (The King and I), so Steinbeck’s north Californian coastal community of amiable social dropouts, drunks and whores might not have been totally unexpected territory.

It’s all stick and no lollipop, a chocolate box stuffed with nothing but empty wrappers: what a walloping letdown this intensely anticipated musical based on Roald Dahl’s perennially popular 1964 children’s book turns out to be.

There is no formula for creating a hit musical. If there were, the history of the West End and Broadway would not be haunted by the many ghosts of bygone disasters. Let us not list them here. The lack of a roadmap notwithstanding, the long-awaited version of Charlie and the Chocolate Factory is ticking all the right boxes.

It opened with a standing ovation. And in a place the size of the 02 – the venue put on this earth to make Luton airport feel better – that’s impressive. It was that kind of evening: not so much Streisand in concert as an opportunity for worshippers at Barbra’s shrine to do a whole lot of basking in her genuinely unparalleled glory. Fifty years at the pinnacle of popular music is not to be sneezed at. That she can sing with a 60-piece orchestra and still deliver shiver-inducing money notes at the age of 71 is truly something. It is not, however, everything.

Fans of this bewilderingly popular musical, and they are legion, will not be disappointed. Director Tom Hooper knows how to tell a fast-moving tale that makes light of the final running time (originally 158 minutes, slightly shorter in this DVD release, which offers no extras. Those who went to the film more than once will, I'm told, miss a couple of scenes). The lighting is appropriately lugubrious, most of the settings convincing – though occasionally there’s too much dependence on CGI – and famously the singing actors perform their numbers on set, often in long takes.

If this native New Yorker were in a relationship with the city of London, our Facebook status would read: “It’s complicated.” We’ve been through hell together. London is one of my favourite cities. I blissfully cross the pond several times a year to teach and to see my mates. But, this fabulous city also bestowed on me the worst reviews I’ve ever gotten in my life. So, why the heck am I coming back to do yet a show about the very show that shattered my dreams? Insane!

In recent years theatre has sought assistance from a pair of popular art forms. Shows based either on movies, or on pop groups’ back catalogues, have become mainstays of the theatrical economy. So the latest musical to open in the West End has the whiff of  boardroom cynicism. What happens when you randomly select a famous film and an iconic songbook, yoke them together and shove them out in front of the footlights?

People sneer at musicals for endless reasons: they hate Broadway brashness, non-naturalistic lurches in and out of song, the sentimentality. One of the least acknowledged reasons, however, is because their plots – predictability plus songs – have zero tension. And you know what? Placed in the witness box, many a musical emerges guilty as accused. But the quietly astonishing Once is innocent of all those charges.