Let’s get one thing straight at the outset: Szymanowski’s 1926 opera Król Roger isn’t a lovely occasional oddity, a rarity whose appeal is largely novelty, or a dust-it-off-once-a-decade sort of piece. It’s that rarest of things, a real and original masterpiece whose worth has been unaccountably undervalued. This new production by Kasper Holten does nothing to obscure its beauty, making a strong case not only for the work’s sensual appeal, but also the larger philosophical architecture underpinning this maverick score.

Judge Judy meets The Only Way Is Essex: this endlessly resourceful production of Gilbert and Sullivan’s first (mini) masterpiece Trial by Jury is one that cries out to appear on TV. Which in a make-believe sense it does: we’re the audience in the studio where Court on Camera is about to air. A warm-up chappie who turns out to be the Usher (Wagnerian bass-baritone in training Martin Lamb) – on other Sundays it will be a lady – gauges our capacity to applaud and boo, and we’re off on a case of breach of promise of marriage as you never saw it before.

There’s a lot to be said for concert performances of Wagner. Not only are you spared the post-prandial lucubrations of aspirant directors – the moonmen and the fighter pilots, the jackboots and the biogas installations. But it’s possible to concentrate on Wagner’s greatest theatrical gift: not his stagecraft or stage imagery, but his management of time and psychological growth through purely musical means.

I do wish that arts institutions would stop using the word “immersive” when they simply mean “staged”. Just to be clear, there is nothing “immersive” about Netia Jones’s new staging of Georg Friedrich Haas's song-cycle ATTHIS at the Royal Opera House’s Linbury Studio, whatever the blurb may say. The director’s signature video projections, dance, song and music, come together to create an exquisite, hypnotic piece of very traditional theatre – not a promenade or a broken fourth wall in sight. And it’s all the better for it.

Even at the tragic heart of Janáček's Jenůfa there is ambiguity. As the Kostelnička or village sacristan takes her stepdaughter Jenůfa’s baby boy outside to drown it in the icy river, you cannot quite be sure whether she is motivated by pride, fear or her love for Jenůfa. In this poised new co-production by Scottish Opera and Danish National Opera, there is no doubt that she is driven by love. Murderous it may be, and it will nearly destroy her, but her compassion cannot be denied.

When does a Gilbert and Sullivan chorus make you laugh, cry and cheer as much as any of the famous set pieces? In this case when Major-General Stanley’s daughters “climbing over rocky mountain” wear pretty white dresses but turn out to be gym-trained showboys from the waist up, with their very own hair. That’s already one extra dimension to an operetta gem, but there’s so much more to enjoy around the crisp delivery of Gilbert’s undimmed lyrics.

A journey into dreams through songs from Dowland to The Kinks; a Swiss director who, Covent Garden’s Director of Opera Kasper Holten assures us, is “one of the most important European theatre artists”; a Norwegian chanteuse who, I assure you, is a performer of real originality. All that should add up to something just a little bit extraordinary, shouldn’t it? Sadly not. What I saw last night was the kind of thing I’d shrug off having chosen at random from offerings at the Edinburgh Fringe.

Composer Tansy Davies and librettist Nick Drake’s opera Between Worlds cannot help but be a devastating tribute to the tragedy of 9/11. Yet the whole is peppered with problems that mean this result is achieved only intermittently. Davies – whose first opera this is – and the playwright Drake, with Deborah Warner directing, have picked a topic that would seem at first glance to demand the scale of a modern-day Götterdämmerung. The result they extrapolate is far from that – but when it does succeed, it is in ways that are not really about 9/11 at all.

There was a moment half-way through Jonathan Dove’s children’s opera Swanhunter when I suddenly realised why pantomime developed its convention of the principal boy. Having a grown man prancing and posturing boyishly for the entertainment of a room full of kids feels odd, affected somehow, distorting the simplicity and sincerity of the tale being told. Which is a shame when, as here, the theatrical trappings are so vivid and enticing.

Still they keep coming, 35 years on from the London premiere of Sondheim's "musical thriller": Sweeneys above pubs, in pie shops, concert halls and theatres of all sizes, on the big screen, Sweeneys with symphony orchestras, two pianos or a handful of instruments wielded by the singers, Sweeneys as musicals and as operas, the dumpy and the tall. Which type was this one? Not a vintage English National Opera production, that much seems clear.