Conductors often acquire epitaphs upon leaving major orchestras — with damning faint praise, like "the world's greatest conductor of Bolero." In the opposite spirit, departing New York Philharmonic music director Alan Gilbert could be called the ultimate interpreter of The Unanswered Question, a Charles Ives piece you don't have to know because the title suggests how Gilbert forges forward for an audience that maybe wished he wouldn't.

Philadelphia knew him when he was a student at the Curtis Institute, a substitute violinist for the Philadelphia Orchestra, and music director of  Camden's Symphony in C from 1992 to 1997, when it was known as the Haddonfield Symphony. Rock-solid in some ways, incessantly probing in others, he's now finishing his farewell New York Philharmonic concerts in what may be the most puzzling music director departure of recent years — even in a world where artistic partnerships resist analysis.

Many pundits say he did all the right things — modern music, standard repertoire, plus staged operas. In a world that’s being dazzled by high-personality Gustavo Dudamel and Yannick Nézet-Séguin, the question is whether Gilbert did them right enough,  with the personal magnetism to pull it off. Or with a fighting spirit,  which, he suggested in exit interviews, was in shorter supply.

He certainly pulled off his final official concert program of the season, which wrapped Saturday at Lincoln Center's David Geffen Hall. Was there some genteel defiance in his choosing, of all Mahler symphonies, the 7th, which is the most gnarled and confounding? Maybe the defiance wasn't so genteel, with him augmenting the orchestra with guest players from Iran and Iraq.

Yo-Yo Ma made a somewhat last-minute appearance Thursday, but not playing Dvorak. Violin in hand, Gilbert joined Ma's cross-cultural Silk Road Ensemble. However much these audiences don't tend to love being thrown a curve ball, this one did. Wynton Marsalis showed up the next night.

Good sport that he is, Gilbert has spent the last week conducting outdoor parks concerts. He is a New Yorker, after all. But doesn't he have other places to go?

Yes. After a succession of appointments — Royal Stockholm Philharmonic Orchestra (2000 to 2008), Santa Fe Opera (2003 to 2006), New York Philharmonic (2009 to 2017) — he is moving his family back to Sweden, where he met his wife, and reportedly has a European position that will be announced this summer. He's also forming Musicians for Unity in partnership with the United Nations to be, as the website puts it, "a presence at moments of challenge and hope." In other words, it's a multinational orchestra that will appear in strategic places, not just to make music, but also a statement about how art crosses borders.

Gilbert tends to leave goodwill in his wake. Ex-colleagues in Philadelphia say he deserves all of his success.

He also earns points for creating career-making moments with an unflashy, hold-back-to-move-forward approach. When he first took on the New York Philharmonic, Gilbert told the Inquirer, "I've tried to let things come out in a natural way and not spill it all at one time. My New York Philharmonic debut program was not the kind of home-run program you might expect. … The way I explain it — and people thought I was absolutely insane — is that I tried to hit a solid double." One program paired Beethoven with little-known Wilhelm Stenhammar. His specialty is Carl Nielsen, a Danish composer whose profile is a notch or two below Sibelius.

His home runs were with modern music. Some conductors do lip service to new music with 10-minute pieces at the beginning of a program. Gilbert went for the huge works that nobody else does, commandeering the Park Avenue Armory for Stockhausen's Gruppen for three orchestras. Ligeti's surreal opera Le Grand Macabre enveloped the orchestra's Lincoln Center home with Eric Owens flamboyantly portraying death at the end of the world. Gilbert also gave the New York premiere of the massive Christopher Rouse Requiem — a piece so big the Baltimore composer wonders whether it'll ever be done again.

So what is the unanswered question? For some, it's standard repertoire. Every conductor pays a price for programming so much modern music, though the blow is softened if Beethoven-to-Mahler concerts are brilliant.

And, for some, Gilbert will never be neurotic enough for Mahler. In contrast to Leonard Bernstein's tortured performances, Gilbert's Mahler 7th didn't leap out in as many directions as possible. Even in the crazy final movement that seems to be eight different pieces cut and pasted together, Gilbert showed how all this music belong together in the same piece — with players of intentionally mixed nationality. Point taken.

On radio broadcasts from the Philharmonic's recent European tour, the Berlioz Symphonie Fantastique and Mahler Symphony No. 4 were quite satisfying, with personal touches that are evidence of a keen relationship with the music. But Prokofiev's Violin Concerto No. 1 with Frank Peter Zimmermann showed what was missing elsewhere: that extra degree of concentration that vanquishes all previous points of reference with the piece.

Maybe that kind of performance happened more often for Gilbert with other orchestras? Certainly, I heard it in a Royal Stockholm Philharmonic broadcast of Bruckner's Symphony No. 8 in 2014 and Shostakovich's Symphony No. 4 with the Juilliard Orchestra this year.

So might the unanswered question be, at least in part, the New York Philharmonic? One loves that orchestra for its flinty edges, the polar opposite of Philadelphia's sonic voluptuousness. Though the players are reputed to be far more cooperative than in the past, they seem like a rather moody bunch. Regular Philharmonic-goers say you should never hear the last performance of a program because the players have mentally moved on. Then you hear the opposite, and the last is the best. What is certain is that this orchestra doesn't give photocopy performances.

Gilbert will be just fine — whatever he goes on to. The New York Philharmonic is bound to have standard-repertoire electricity with his successor, Jaap van Zweden. If questions about the end of this affair remain open, it's because possible answers are so numerous.