Prima Donna, Manchester Festival, Manchester<br/>Queras/Hadid, Manchester Art Gallery, Manchester<br/>L'incoronazione di Poppea, Opera at Iford, Somerset

A pop of Puccini, a spritz of Strauss, a shot of Massenet and a generous measure of Poulenc. Serve with a twist of Canteloube and a garnish of Brel and you have Prima Donna, Rufus Wainwright's nostalgic tribute to, well, several things.

The first is opera itself, which the songwriter treats as a dressing-up box, clothing his bittersweet, ambiguous melodies in vintage histrionics. The second is divadom, exemplified here in the role of the reclusive soprano, Régine Saint Laurent, a composite of Maria Callas, Gloria Swanson, the nameless heroine of La voix humaine and the second Mrs Charles Foster Kane. The third is Paris, a city where umbrellas are shaken dry to a frisson of tuned percussion, and past glories are recalled to the 12/8 tattoo of a Piaf chanson. The fourth, I suspect, is Wainwright's childhood, when he and his sister Martha would act out Tosca to escape from the well-documented complexities of Wainwright family life.

Set in 1970, Rufus's opera traces a day in the life of Saint Laurent (Janis Kelly), whose encounter with "Paris's top journalist" (William Joyner) forces her to confront the memory of the night she lost her operatic moxie. Silent for six years, protected by her maid, Marie (Rebecca Bottone), the grotesque factotum, Philippe (Jonathan Summers), and his mute sidekick, François (Steve Kirkham), Saint Laurent is preparing to return to the stage, in the role that made her famous (cue the Act II dream sequence, with its echoes of Massenet's Esclarmonde). Bewitched by Boulez as Paris was in 1970, it seems unlikely that the city's top journalist would interview a retired diva. But never mind.

After 90 minutes of heart-on-sleeve emotionalism, Prima Donna switches personality – pricking the opalescent bubble of a reference to Der Rosenkavalier with a joke about autograph hunters, archly inverting Butterfly's "Who is that woman?" as the journalist introduces his Japanese fiancée, and ending with a blast of the Marseillaise and a burst of Bastille Day fireworks. Cute.

Is Wainwright guilty of having his patisserie and eating it? You bet. If the score teeters colt-like between Romanticism and Neo-classicism (with a base-note close to Allan Gray's scores for Powell and Pressburger), if its orchestration is uneven and its melodies awkwardly pitched, Prima Donna's deepest flaw is a plot that could have been written by a precocious child, then revised by an adult who is anxious to prove his sense of irony.

This painful juggling of sincerity and artifice is the curse of the entertainer. Strauss, for one, was not above the same tricks. But talented songwriters are not always the best opera composers. Of Schubert's 16 attempts, only Fierrabras has enjoyed sporadic revival. And were Wainwright not already a successful recording artist, his first commission would have been a 10-minute short, his second a one-acter for an artist development programme, his mainstage debut (if he was astonishingly talented and astonishingly lucky) at Aldeburgh.

For all my misgivings about Manchester International Festival's commissioning policy (festival director Alex Poots was responsible for Damon Albarn's Monkey and, while at ENO, Asian Dub Foundation's Gaddafi), director Daniel Kramer delivers a handsome show. Lit in lime green and flamingo pink by Peter Mumford, Antony McDonald's designs move seamlessly between the silvered walls of Saint Laurent's apartment, Marie's kitchen, a vertiginous balcony, a cramped dressing-room and the stage of the Opéra Garnier. Sealed off behind perspex, the soundless violence of Marie's husband and Saint Laurent's silent scream are the most dynamic moments.

Though the Orchestra of Opera North sounds uncomfortable with some details, the tempi rarely flag under Pierre-André Valade. While Summers growls and howls and Joyner wrestles a tessitura that runs from baritone to haute contre, Bottone sweetly turns her aria "A mon pays de Picardie". Kelly is magnetic throughout: commanding in chest register, wistful in "Quand j'étais jeune", sometimes girlish, sometimes crone-like. Nonetheless, it is ironic that such a hard-working real-life prima donna should be playing this caricature of a diva as though it is the role of her life.

So from music that craves attention to music that needs no audience. Mirrored in the frozen curves of Zaha Hadid's architectural installation, Jean-Guihen Queyras's recital of Bach's Cello Suites in G, E flat, D minor and C unfolded as though in perfect solitude. Antithetical to the dance-like Suites of Alison McGillivray and Steven Isserlis, Queyras's Bach is meditative, analytical, comfortable in its melancholy. Both approaches work. Aside from a tendency to exaggerated triplets, this was an eloquent, understated performance, topped off by a breathtaking encore of Kurtág's crystalline, fragmentary Az hit ("Faith").

Martin Constantine's production of L'incoronazione di Poppea for the Early Opera Company at Iford Manor was strangely diffuse and unfocused. Fellini was supposedly the touchstone, yet the most cinematic image was reserved for "Pur ti miro", as the faces of Monteverdi's languid Poppea (Katherine Manley) and crazed Nero (Nicholas Sharratt) were caught by flashlights held by Fortuna (Doreen Curran), Virtu (Joanne Boag) and Amor (Daniel Keating-Roberts) then plunged into darkness. Though much of the individual singing was strong, and the orchestral performance meticulously shaped and coloured under Christian Curnyn, characterisation was thin, design minimal. Those who didn't know the work will have been mystified. Those who did, struggled.

'Prima Donna' (0844 815 4960) ends today, 3pm; transfers to Sadler's Wells in spring 2010