There will doubtless be stuck-up sticks in the salmon mousselline who’ll disagree, but I’m all for the Opera Australia’s bold move to loosen the noose-like definition of opera a little. Or a lot. I’m all for charting a new, diversified course: after all, if jazz can get into bed with rock, why shouldn’t opera get into bed with the likes of musical theatre? And if you’re going to be promiscuous and play fast and loose with your definitions, you might as well share a pillow with Sondheim. In any case. What is opera if not a drama set to music?

The timing of OA’s production of A Little Night Music could hardly be more redolent, with a first-ever Broadway revival currently wowing audiences (and winning Tony awards). ‘Our’ version gives no quarter when it comes to celebrity or giftedness.

Sigrid Thornton (pictured, left) stars, as beautiful actress Desiree Armfeldt (what a stretch). There is a sense in which, of course, everyone awaits the centrepiece of the show, Send In The Clowns. All roads lead to it. The fact that Sigrid, not known as a singer, would be performing it brought added anticipation, curiosity, voyeurism and piquancy. Would the tall poppy of the small and big screens fall over? Uh-uh. Okay. She isn’t a singer. But in the same way Audrey Hepburn steeped Eliza in so much charisma, one couldn’t help but be drawn to her, hanging on her every word. Yes, my long-beloved, admired-from-afar Sigrid brought meaning, timing, feeling and drama to the song in a way I’ve not seen or heard before.

Of course, Sondheim himself has helped her, in writing the song for an actress, rather than a singer, in the first place. She even seems to have chosen to emulate Eliza’s overly rounded tones, which works a treat. Sigrid seems to exploit this new platform for her talent and skills to show, unequivocally, just how much she’s blossomed as an actor, since her magnetic early years; not least, of course, in the sweeping romance, The Man From Snowy River. Anyone who’s caught even a glimpse of her ‘broad’ role in Underbelly, and who then sees her in the opera theatre, will see just how jaw-droppingly versatile she’s become.

By her side is LNT (Living National Treasure) Anthony Warlow (pictured, right), still with a seductive voice of great and undiminished quality, character and clarity, as Desiree’s diehard lover, Fredrik Egerman. He’ll soon take to his role as the Pirate King in OA’s Penzance: quite a transition; and he gets to have luxuriant hair, once again, in both roles. Siggy and Ant make a power couple.

Roger Kirk’s hand, and eye (for they coordinate seamlessly), is all over this. The stage is tasteful and dreamlike: sheer curtains depict stately trees and foliage; a fairytale, deliberately faux, Disney-style ‘flatpack’ mansion sits at the back of the stage; sets rotate on the larger-than-life lazy susan, which also affords the illusion of movement as people walk on by. The front ‘wings’ aren’t ignored either. His costumes are elegant, opulent, chosen from an exquisitely complementary palette; period, with a sense of the comical (they parody the wearer, even while adorning). His is a significant contribution, realising the ‘delicious sophistication’ for which the work is renowned.

Director Stuart Maunder has made inspired casting decisions. As well as the double-whammy star power of Thornton and Warlow, he brings us Dame (well, she ought to be) Nancye Hayes, as high-minded matriarch, Madame Armfeldt. She is, inarguably, a living national treasure (which, in her case, means much more than merely being a woman of a certain age), whether officially so or not, and shows why, with a resplendently proud and haughty performance.

Katrina Reallick, as Countess Charlotte Malcolm, is a brilliant young artist still in ascendancy, despite already having a wealth of experience. She easily manages to be utterly convincing, as the hard-done-by wife of the vainglorious Count Carl-Magnus Malcolm, an incorrigible military man, played and sung to powerful perfection by tall, dark and handsome Ben Lewis. From WAAPA to the University of Sydney; ATYP to McLeod’s Daughters; Priscilla to Sondheim. That’s been his journey. Or part thereof.

Shameless nepotism? Shameful? Or judicious casting. Somewhere in-between? Well, ignore the name Maunder, after the name Lucy, and you’ll be impressed, too, methinks, with her performance as Anne Egerman, very nearly childbride of Fredrik (good thing he’s a solicitor, and not only of young women). The test, and fact, is she’s delightful: by turns, or all at once, innocent, charming, coy, clueless and lovable. And beautiful. Perhaps you saw her in The Eternity Man.

Matt Robinson is Henrik Egerman, the sexually repressed and naive aspiring priest, who can’t quite contain his burgeoning hormonal impulses, which extend to more than one object of desire; both prohibitive and inappropriate, and not only because of his unsuitable vocation. He, too, is very credible as the late-blooming, somewhat oppressed, overshadowed, mocked and tormented son of Fredrik. You might’ve caught him in The Pacific.

The last is yet another ad for OA’s vision in recruiting stage and screen actors, cabaret artists and musical theatre veterans to the traditionally more rarefied realm of opera. How long overdue it is these barriers be torn down, for they’ve been as restrictive, unjust and redundant, artistically, as the Berlin wall was, societally.

Kate Maree Hoolihan, yet another WAAPA prodigy, is Petra, saucy maid in the Egerman household. Her ample bosom is not just for show, as it upholsters magnificent lungs: she’s a stunning singer, with a self-assuredness not necessarily typical of one of relatively tender years.

Erica Lovell makes her OA debut as Fredrika, daughter of Desiree, raised and steeped daily in worldly wisdom by her grandmother, and learning fast. She treads the line between the innocence of childhood and knowing cynicism of womanhood finely, integrating both into her character.

Anthony Lawrence is a good fit, as Frid, Madame’s powerfully-built manservant, who falls in lust at first sight with the prodigious Petra. He and his belle are the epitome of earthiness, amidst the rarefied, intangible follies, fancies and fascinations of the idle rich for whom they toil.

Katherine Wiles, as Mrs Nordstrom; Jane Parkin, as Mrs Segstrom; Jacqueline Dark, as Mrs Anderssen; Kanen Breen, as Mr Erlanson; Byron Watson, as Mr Lindquist. All accomplished. All faultless. How often can one say that? And Andrew Greene ensures the orchestra performs its supporting role flawlessly as well; as does chorusmaster Michael Black with his charge. John O’Donnell’s sound design ensures clarity and perspective, while Trudy Dalgleish’s lighting complements the other design elements superlatively. Elizabeth Hill’s choreography made non-dancers look dancerly (notwithstanding a happenstance slip by Ms Thornton, which nearly saw her go arts over Titania, as it were).

Know the story? Sweden. Turn of last century. Three generations come together for a glorious midsummer weekend in the country, under a sun that never sets. The sun, of course, serves to illuminate what a complex web of intrigues they’ve woven. Hugh Wheeler’s book mocks the self-indulgence of the well-heeled to the nth, bolstered by Sondheim’s lyrics. Take Now, for example, in which Fredrik, returned home for his afternoon, er, nap, muses to himself over whether or not to do just that, or assail his lovely wife. ‘Now, there are two possibilities: A, I could ravish her; B, I could nap.’ Then, it’s a question of ‘say it’s the ravishment, then we see the option that follows, of course: A, the deployment of charm, or B, the adoption of physical force.’ Germaine Greer might have something to say about that, but she’s not written into the ‘opera’. But while Petra’s aspirations may be simple and humble (‘I shall marry the miller’s son: pin my hat on a nice piece of property; Friday nights, for a bit of fun, we’ll go dancing!’), Anne has more smarts than the sweet imbecilities for which her husband gives her credit, in interpreting her rival’s motives (‘No, the ghoul! She may hope to make her charm felt, but she’s mad if she thinks I would be such a fool as to weekend in the country’). Sondheim draws characters, male and female, with such delicious knowing and precision.

Vocally, Lewis, Warlow and Hoolihan will blow you away, but there are others hot on their heels, like Ms Maunder, not to mention the fine voices of the supporting cast. Hayes, Lewis and Thornton are charismatic and probably take out the key acting honours, for mine. But the fact I’m having difficulty discerning the standouts is testament to the excellence, through-and-through, of this production. The critic arrives, supposedly, eager, hungry to find fault, in an ‘aha!’ moment. (Hey, it’s a hobby!) Alas, in the Australian Opera’s A Little Night Music, I could find none. Isn’t it rich? Isn’t it bliss? Artistically, aesthetically, musically, dramatically, lyrically, sonically, visually and otherwise, it’s a resounding ‘yes!’ Don’t you approve?

The details: A Little Night Music plays the Sydney Opera House until July 15. Tickets on the Opera Australia website.