Near the end of its 2014 Next Wave festival, at the weekend the Brooklyn Academy of Music (Bam) presented The Etudes, marking the first time all 20 of these solo piano compositions by Philip Glass have been performed in a single evening. Glass wrote in the program notes that he composed them “to explore a variety of tempi, textures, and piano techniques”, but he also told me when I interviewed him in 2012 that he wrote them to become “a better player”.

The Etudes fit into a recent trend, which started when Glass turned 75, of having the rare chance to finally see his large-scale works in their entirety. Watching 10 pianists play all 20 Etudes in one evening is obviously not for those whom Glass’s structures drive crazy; nor is it either necessarily for the casual Glass fan, like those who made Symphony No 9 a bestseller on iTunes. It is for people like me, for whom seeing all four hours of Music in 12 Parts or all five hours of Einstein on the Beach is our idea of a good time.

Glass started composing the Etudes in 1991 (around the time he was making Hydrogen Jukebox with Allen Ginsberg and scoring A Brief History of Time with film-maker Errol Morris) and stopped in 2012 (when he composed Orbit for cellist Yo-Yo Ma and street dancer Lil Buck; the Walt Disney-inspired opera The Perfect American; and his 10th symphony). In between there were works as varied as string compositions for the Kronos Quartet, to scores for films from The Truman Show to Candyman II.

Nico Muhly, the composer of the opera Two Boys, performed some of the Etudes (the creepily haunting No 5 and harder-driving No 6 the night I saw the performance). He also was the musician “in charge” at the historic performance of Four Organs at Bam earlier this fall, when Glass and Steve Reich played on the same stage for the first time in 30 years after an infamous falling-out. Muhly was once an intern in Glass’s studio, later moving up to being the person to program Glass’s hand-written scores into a computer.

Muhly told me last week that working for Glass taught him “what it means to be a responsible member to the community of musicians” – Glass is known as being a generous composer and collaborator when it comes to the business of making art – and that he found Glass had “a spirit of benevolence which is rare in composers”. Muhly says Glass’s Etudes represent a “big overview of his harmonic language”.

“When I was working for him,” Muhly said, “you could see things from the Etudes form the germ of an idea. The fun of an Etude is that it’s a study. It’s designed for technical or harmonic obsessions.” All of them, he said, are “little diagrams of where his head is at the time”.

Seeing the progression of a couple of decades of those diagrams compressed into one sitting was incredibly satisfying. In the same way I feel happy to be a reader while Toni Morrison is writing, I have felt incredibly lucky to be alive while Glass – to me, arguably the most important American modern classical composer – is working. It’s great to see the work as it comes out whether I love it or hate it. Ever since I talked to him about mortality – Glass doesn’t “have retirement in mind in any way at all” – I often wonder each time I see him play whether it could be for the last time. He does carry a performance schedule that puts musicians less than half his age to shame. But when I saw Glass perform at the 2,000-year-old Temple of Dendur a couple of years ago, I had the distinct sense of the fleetingness of time, and a sense that, while his music will last, the man himself (like all of us) has a finite number of days on this earth.

The Etudes drove this home. Nos 1 and 2, played by Glass both nights, are relatively gentle, like a lullabies. (Indeed, I have listened to No 2 and Mad Rush often as I’ve fallen asleep.) The charge and drive largely get more aggressive and passionate as the numbers increase into adulthood, conjuring comparisons to Gershwin and Copland. It is hard to imagine falling asleep during No 10, played and ended with a particular flair on Friday night by Timo Andres. But by No 20 (played on Friday night by Maki Namekawa, who totally became one with the music), the Etudes have again slowed down to a Schubertian pace, ending so gently that silence and sound nearly blend into one another – much the way old age, if achieved, can render the elderly as calm as a baby again, as life and death overlap.

As satisfying as seeing the work was the ethnic and musical diversity of the performers. I talked to Glass in 2012 about the lack of racial diversity in “‘art music”, growing up in his father’s record stores in Baltimore (“The city may have been segregated, but my taste in music wasn’t”) and how he has dealt with race in his own work. Diversity on stage isn’t unusual with Glass (as in his opera the CIVIL warS, the Helga Davis lead role in Einstein, and the inclusion of bands like Das Racist at his annual Tibet House fundraiser). Still, these are exceptions in this world, and it was great to see the solo piano of one of our most important living composer interpreted not just by white male performers but by Namekawa as well as Aaron Diehl (an accomplished jazz pianist who has toured with Wynton Marsalis), Tania Leon, Sally Whitwell and Jenny Lin.

The two most disappointing things about the performance were the venue and the performance by the composer himself. BAM is a cultural institution which, regarding its programming in a wide variety of arts, is unparalleled in quality not just in New York City but in the entire United States. Yet its Howard Gilman Opera House was not an ideal setting for a solo piano concert of Glass’s work.

Even sitting relatively closely, I found myself straining to hear the piano in the cavernous opera house, distracted by many other shifting listeners and the sound of sirens seeping in from outside, probably coming from the NYPD following Eric Garner protesters. (Not that Glass would have minded this juxtaposition of high art and street protest, necessarily: he famously gave a “mic check” to Occupy Wall Street protesters gathered outside his opera Satyagraha at Lincoln Center in 2011.) I could only imagine how much more moving it would have been to hear these works in a setting like Carnegie Hall – the kind of venue with acoustics that illuminated the subtlety of the second movement of Symphony No. 9 in its American premiere in 2012, or Glass at the keys himself with violinist Tim Fain in Pendulum for Violin and Piano.

Regarding Glass playing No 2 (which, according to my own iTunes account, is the piece of music I listen to most often): I should qualify my disappointment at hearing my favorite composer play perhaps my favorite piece of music. Glass’s technique did seem to be softening, and he didn’t seem nearly as sharp as when I last saw him play No 2 in a program with Patti Smith a couple of years ago; nor did he seem to have the boundless energy with which he kicked serious ass in playing the hell out of Music in 12 Parts, for hours on end, that same weekend.

But there is something sweet, if melancholy, in seeing Glass slow down a little as he approaches 78. A choreographer can’t dance their own work forever, but that doesn’t mean it’s any less important. No matter how much I may admire Glass as a performer, his legacy will be primarily as a composer. Indeed, he composes precisely so that Muhly and Diehl and others can perform his work, in ways technically and artistically different than he ever could, but also performers not yet born.

And so, his work will outlast not just his hands and the hands of the pianists playing them this weekend, but my own ears, too – and yours. It works best, therefore, to think about the Etudes as akin to the Metropolitan Museum’s 2003 show on Leonardo Da Vinci’s notebooks: as the sketches of a creative force whose work will outlast any single one of us, including the artist who made it.

• The 20 Etudes will be performed in full again at the Barbican Centre in London in April 2015