Unlike Schubert, Mendelssohn and Shostakovich, Mozart composed nothing astoundingly individual before the age of 20. That leaves any odyssey through his oeuvre, year by year – this one will finish in 2041, by which time I’ll be nearly 80 if I live that long – with a problem effectively solved by Ian Page and his Classical Opera in placing works by contemporaries of various ages alongside young Amadeus’s efforts.

It’s never funny like Ligeti’s Le grand macabre, though it touches on that joke apocalypse’s more nebulous soundscapes. Nor is it obviously dynamic like David Sawer’s From Morning to Midnight, with which its title is not to be confused (there are no transitional stages here, only birth and death). Wagner’s cosmic sweeps don't entangle the banal with the numinous like this. So what exactly is the new opera Morning and Evening?

Not a ray of sunshine illuminated the landscapes that were explored in this stormy programme, the first of a three-part history of the Celts. It aimed not only to show the latest investigations into the Bronze and Iron Age tribes who inhabited Europe from Turkey to Britain but to suggest their culture was richer than the simple cliché of barbarians at the gate.

In 2007, Jiří Bělohlávek set the distinctive seal on his leadership of the BBC Symphony Orchestra and their ongoing Mahler cycle with a riveting performance of the Third Symphony. The legacy he established of a deep, well-moulded string sound which the orchestra didn’t really have before has left its mark on his successor Sakari Oramo’s even more impassioned attempt at the most epic of all Mahler’s symphonies.

Nothing will ever test the depth, breadth and sheer virtuosity of a large orchestra more than Mahler’s symphonies. It’s hardly surprising, then, that the two unsurpassable concert experiences, for me, have been Bernstein’s Mahler Five at the Proms and Abbado’s Lucerne Festival Ninth, or that the two London orchestras with the most consistently challenging conductors, the LPO under Vladimir Jurowski and the BBC Symphony Orchestra with Sakari Oramo, have chosen to open their new seasons with the two most experimental of the 10 symphonies on consecutive nights.

Every Proms season needs a late-romantic rarity to envelop its audience in a bewitching spider-web of sound. This year’s candidate was of more than passing interest, the incandescent Second Symphony of Franz Schmidt, scion of the Austrian Empire – born in what is now Bratislava, three-quarters Hungarian, an embattled cellist in the Vienna Philharmonic during Mahler’s tenure. The orchestra now wants to do him proud again, thanks to the very centred championship of Semyon Bychkov. And Schmidt’s music has the virtue of not being over-familiar to the Viennese players, unlike Brahms’s.

In a curious deal, two operatic card games were running almost simultaneously last night. At the London Coliseum, Tchaikovsky’s outsider Hermann was gambling for his life on three hands of Faro in The Queen of Spades, while in home counties countryside, Robert Storch aka Richard Strauss thought he was relaxing from a performance with a nice game of Skat when in comes a telegram from his tricky spouse Christine, aka Pauline Strauss, unsigned as usual, accusing him of adultery.

It’s not often that you arrive for a piano recital to see members of the audience on the stage, clustering around the instrument and taking photos of it. Those curious about the newly unveiled, straight-strung Barenboim-Maene concert grand (the name above the keyboard is simply BARENBOIM) were periodically ushered away from it; it was closed and reopened several times before it was time for the maestro himself to take control.

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 by trumpeters’ standards, Håkan Hardenberger is a flamboyant figure. He sports a sharp, tailored suit and a wing-collared shirt, and his stage presence is all swagger and pomp. HK Gruber has captured his spirit perfectly in his jazzy, experimental trumpet concerto Aerial, which has become the trumpeter’s calling card. That proved the highlight of the evening here, though, as it was followed by a lacklustre Mahler Five, a rare disappointment from the usually reliable conductor Andris Nelsons.