Valery Gergiev’s exploration of the music of Karol Szymanowski is one of the most vitalising series mounted at the Barbican in recent years - to compare, say, with Sir Colin Davis’s Sibelius and Berlioz, Michael Tilson Thomas’s tributes to Leonard Bernstein, or Gergiev’s own Shostakovich and (increasingly) Prokofiev.

Valery Gergiev is a human dynamo.

Philip Glass is sufficiently famous that his 75^th Birthday celebrations have been going on all year (he was actually 75 in January) and the year saw two of the absolute highlights of his career presented at the Barbican. His first opera Einstein On The Beach and last night, the soundtrack to his first film score Koyaanisqatsi, performed alongside the film itself, with Glass on keyboards. More of his “greatest hits” will be performed at the Union Chapel in Islington tonight.

If you’ve ever wondered what a bad day at the office looked like for Handel then look no further than Belshazzar – an oratorio that positively demands heavenly intervention and possibly a bit of smiting. With a first act that worried even the composer with its length, a confused magpie plot and a libretto whose worst excrescences outdo even those of Congreve’s Semele, it’s one of those neglected works that gain little by being dragged out into the light, even by such distinguished champions as William Christie and Les Arts Florissants.

Say what you like about America, but it certainly knows how to turn out an opera diva. While the Russians and even Italians can be chilly and untouchable in their splendour, there’s a cultivated ease with the likes of Renée Fleming and Joyce DiDonato that allows a song recital to be both a relaxed conversation with an old friend and a piece of highly crafted technical showmanship. It’s artifice and artistry of the highest order – not just making it all look easy, but showing us just enough mechanics to prove that it definitely isn’t.

Her Majesty was making a rare concert-hall appearance to present the Queen’s Medal for Music, and any little Englanders in the audience might have been tempted to link royalty to Elgar’s Enigma Variations. But conductor Robin Ticciati, with a generosity and wisdom beyond his 29 years, raised this orchestral masterpiece to the universal level it deserves. Elgar’s "friends pictured within" trod air and revealed every aspect of their often shy, beautiful souls.

Now the BBC Symphony Orchestra’s second Conductor Laureate, Jiří Bělohlávek was always going to deserve a hero’s welcome for taking his players to the finishing line of their six-year cycle through Mahler’s symphonies. As more superficially brilliant Mahler series like Gergiev’s, squeezed into a single anniversary season, seem a distant memory, many of Bělohlávek’s slow burn, deep vein interpretations live on in the mind and soul.

Leonidas Kavakos was originally meant to be premiering a concerto by Argentinian composer Oswaldo Golijov, which had also been scheduled for Berlin in 2011 and subsequently for Los Angeles in May this year. The composer missed both those deadlines and the work apparently remains uncompleted – it was replaced on the programme by the Berg concerto.

There are always risks involved in the uncompromising side of the BBC Symphony Orchestra’s family-friendly concerts. Succulent slices of fox-meat in the form of a suite from Janáček’s The Cunning Little Vixen gave the kids a nourishing start, and Rimsky-Korsakov’s Scheherazade was always going to seduce them with her effervescent narrative, especially given Czech conductor Jakub Hrůša’s youthful instincts to paint big, bold pictures.

Why is music? A child’s question, a great question. One answered by Evgeny Kissin’s piano recital at London’s Barbican Centre last night, where you might want to engage analysis and come up later with answers but what happened was that you left the concert hall feeling more alive, emotions retooled, spirit lightened, range widened. Music is because. Why else would Beethoven compose 32 piano sonatas? What possible purpose of Haydn to write 62 of them? Because.