To some, Beethoven’s Missa Solemnis is one of the greatest works in the world. To others, it’s kind of a mess. No, wait, scratch that, because I am both of those people, holding both of these perhaps seemingly contradictory views. And Michael Tilson Thomas may be, too, because he has set out to create a version of Missa Solemnis that can explain itself to the people who don’t get it.

You don’t mess with Beethoven. But the San Francisco Symphony is doing just that. They’re currently embarked on a three-week Beethoven festival, and if the idea of a Beethoven festival sounds on paper like what every other orchestra in the world is doing, San Francisco’s stands out. Just the fact that they’re recreating the legendary 1808 concert at which the composer presented the premieres of both the fifth and sixth symphonies, plus the Choral Fantasy, plus the Fourth Piano Concerto — more than four hours of music — makes it worthy of note. And MTT’s Missa Solemnis, which he performed here this week, is plenty noteworthy, too: not only is it semi-staged, as conceived by the conductor himself, but it makes actual adjustments to the score. There is, for example, a boys’ choir. And an additional quartet of vocal soloists, two men and two boys.

And, yes, it works.

First of all, this production (a co-commission with the Los Angeles Philharmonic, where it was performed in January) exploits something that becomes ever clearer in this age of orchestral experimentation: having musicians move around the stage is a fantastic way to humanize the experience. Introducing even a modest amount of physical drama breaks up the perception of the monolithic and impenetrable that proceeds from the sight of a massed wall of black-clad instrumentalists and choristers facing the audience. Instead of An Orchestra and A Chorus, you start to have people; and that in itself becomes a powerful context for a work that is about faith, and questioning it, and having it. The performance is no longer something that is done to or for the audience: it is an experience visibly undergone by the people on stage, as well. And when a boys’ choir comes bursting onto the stage to start the Gloria, it becomes a visualization: the explosive exuberance of the music made flesh.

Secondly, the video projections actually support and enhance the music, rather than, as is so often the case, overwhelming it. Above the stage a ragged screen is rent into quarters by means of a jagged tear in the crude shape of a cross; the screen’s edges splinter into myriad small surfaces, some of them individual screens, some panels of lights. The effect is of stars, and of things coalescing and coming apart, a theme continued in the mainly abstract videos: individual letters flying free, and spinning around, little shards of light, fragments of meaning. There are images that evoke the Gothic arches of cathedrals; and there are even, during the Credo, tracings of glowing outlines of a Christ figure, which skirted awfully close to literalism for my taste, even if the point, of these as of the whole exercise, was to illuminate the music’s intent.

The key question for many listeners, though, is whether anyone has the right to tinker with the scores of what we’ve come to accept as the canon. But it seems to me that this question has effectively been answered over the years: with arrangements of great works for different instruments, or with reductions of important scores, or with restagings and abridgements of operas. Is adding a boy’s choir to the Missa Solemnis (singing, of course, the music Beethoven wrote for sopranos and altos) philosophically really different from creating a chamber version of Mahler’s “Lied von der Erde?” — or, indeed, less different, since it doesn’t actually tinker with what the composer wrote?

Part of the answer depends on the execution, and Thursday night’s was pretty fine. The orchestra sounded great: lithe, responsive to Tilson Thomas’s eager gestures, as lights pulsed and glowed in response overhead. The San Francisco Symphony Chorus sang firmly and mostly cleanly, even when moving around the stage; and the Pacific Boychoir got across the youthful energy that was called for without affectation. And the quartet of soloists, asked to walk a fine line in conveying a sense of drama unfolding without actually manufacturing something that wasn’t present in the music, sang operatically, in the best sense: the tenor Brandon Jovanovich often sounded downright heroic, though at times a little bleaty; Sasha Cooke, the mezzo-soprano, offered a full, warm, solid sound; Joélle Harvey, the soprano, was taut as a high-wire; and Shenyang (just heard in the Washington National Opera’s “Cinderella“) sang with a soft-grained buttery quality that offset the inherent darkness of his bass, but was often too gentle to carry over the group. In the Benedictus, concertmaster Alexander Barantschik left his seat and joined the four singers: five soloists, intertwined.

Admittedly, the last part of the piece seemed less riveting than the first; whether because the freshness of the ideas waned, the novelty wore off, or this is in the nature of Beethoven’s score. The end seemed confused and anticlimactic; the chorus milling to get off stage, a sense of unfulfilment, a hall plunged into darkness. In his extensive and illuminating program note, however, Tilson Thomas indicated that this was exactly what he wanted. “And then it’s time to go,” he wrote, of the work’s conclusion. “Our visit to the cathedral is over. There will be no grand symphonic ending… the orchestra makes a few perfunctory final gestures, and we are at the end.” He achieved exactly this effect, and the result was just as dislocating: finding yourself out in the world again, in the normal light of day, not quite prepared, wondering if it was really over.