There was very little not to like on the National Symphony Orchestra’s program on Thursday night, but there was an awful lot of it.

Let me unpack that sentence, which is stuffed almost as full as the Kennedy Center Concert Hall stage was stuffed with instruments for an opulent program of Romantic, late Romantic, and very late Romantic works led by James Conlon.

Conlon has made it his life’s work to restore to the repertoire music that has languished unperformed since the Nazis proscribed it. More precisely, he’s devoted himself to composers who were impacted by the Third Reich. The two main composers on the NSO’s current program, Alexander Zemlinsky and Erich Wolfgang Korngold, immigrated to the United States to escape the Third Reich; Zemlinsky died here half-forgotten in 1942, while Korngold became a successful, indeed seminal, composer of scores for Hollywood films.

But neither of the works performed were actually proscribed by the Nazis. The Korngold violin concerto was written in 1947, after the “Thousand-Year Reich” had lived out its 12-year span. And Zemlinsky’s “Die Seejungfrau” (The Mermaid) was withdrawn by the composer after a single performance in 1905. The piece’s three movements were reunited only in the 1980s, and this performance was the first in the States to restore to the score 80-some measures of music, about two minutes’ worth, depicting the sea witch who enables the mermaid to change her tail to legs (a painful process).

Unfamiliar music — even led by a well-known conductor such as Conlon and with the ever-sunny Gil Shaham as the violin soloist — is not a big draw for audiences, at least on a balmy spring evening. There were gaping rows of empty seats throughout the auditorium. Which, in a way, was too bad, since the program offered lots of everything that fans of generic classical music like: beautiful sound and opulence and tunes and a sense of grandeur and even, in Korngold’s concerto, literal excerpts from classic film scores.

The program was presented in defiance of the usual order, or in reverse: “Die Seejungfrau,” the biggest and most symphonic piece on the program, came first, followed by an intermission, followed by the concerto, which led to Brahms’s “Variations on a Theme by Haydn,” a 20-minute piece that at many concerts would have been the curtain raiser. The reason for the order was presumably to keep the audience from leaving before the Zemlinsky work, which was clearly Conlon’s chief interest. He even spoke about the work from the stage, conveying his excitement about this music perhaps even more effectively in words than he did in leading the overstuffed music.

Zemlinsky’s “Mermaid” is anything but little; it’s a big tone poem in the Strauss tradition, only longer, clocking in at about 40 minutes. For such a big, unfamiliar work, it goes down easy: You get the story of the mermaid, with Nurit Bar-Josef’s violin in the title role and David Hardy’s cello as the human prince she loves, and lots of coloristic water effects and tone painting — the jolly music of the prince’s wedding to another woman interspersed with sad-mermaid music, for example. It does all this on a large scale with adroit and effective orchestration, but though it is supremely accomplished, it is not altogether inspired. Or perhaps it was just Conlon’s workmanlike conducting. In any event, the piece was perfectly enjoyable, but it isn’t quite meant to be enjoyable, and “innocuous” is not an auspicious description of a huge, symphonic work.

In Shaham’s hands, the Korngold concerto sounded mostly delightful. Shaham has a way of making everything sound delightful; I have a weakness for his meltingly sweet tone, which sounds like a throwback to the 1930s. At the rare moments when his pitch does waver slightly, it sounds downright astonishing since most of his playing is so true. His approach certainly did more justice to the concerto — which flirts along the line between serious and entertaining music that was a leitmotif of this composer’s post-Holywood work — than a more earnest reading tends to do: as if giving the music permission to enjoy itself.

By the third large-scale, opulent piece, the evening had begun to feel a little blowzy, though Brahms’s classicism shone through, in comparison with the other two works, loud and clear. The NSO sounded relatively expansive on this evening, its strings rich, but the Brahms — based on a somewhat driven theme (not, incidentally, actually by Haydn) — had a plodding air about it, perhaps simply because so much had already happened by the time it came around. Still, it was a refreshing program, and one that clearly meant something to the conductor, and the audience appreciated it.

The program repeats Friday and Saturday.