NEW YORK - Fleeing audiences leave varied attitudes in their wake. Some stomp with disgust. Others run in fear of the oblique.

But at the U.S. premiere of Shadowtime by composer Brian Ferneyhough and Penn English professor Charles Bernstein on Thursday at the Lincoln Center Festival, 15 percent crept out early with quiet respect, as if to say, "This may be great but I just can't take it anymore."

Daunting indeed was this dense meditation on the life of the great 20th-century thinker Walter Benjamin, who committed suicide in 1940 while attempting to flee the war in Europe. The opera, which ended its two-day run yesterday, dispenses with that situation during the first scene, and then follows this aesthetic philosopher on an imaginary journey into a netherworld of time and space that is, well, shadowtime.

Imagine a score with enough music to fill out Wagner's 16-hour Ring cycle but compressed into 21/2 hours, without a linear plot. Then contemplate the theatrical sense of making the second scene a 15-minute guitar concerto with slide projections of European train schedules. Or later dispensing with theatrical action in favor of a dense piano sonata played while the performer, Nicolas Hodges, shouts enigmatic reprimands. Or a journey into the underworld where Adolf Hitler and Joan of Arc are on hand but with not much to say.

Clearly, it's a work with its own rules. How well those rules could be understood depended on how often your brain went into overload amid a plethora of musically microscopic details that arrived with little of the usual symmetry and repetition that help you keep track of the big picture. The performers from Neue Vocalsolisten Stuttgart and Nieuw Ensemble Amsterdam, under the direction of Jurjen Hempel, faced almost unimaginable challenges valiantly.

Yet how can you fault a composer whose creative invention runs so relentlessly high? If there was a reward, it came in the final 20 minutes when the music entered the realm of computer-generated sound, and soared in a state of happy liberation from acoustically generated notes of music.

So many opera librettos are ragtag, derivative poetry, but not Bernstein's: His includes 147 footnotes plus quotes from Benjamin and his contemporaries, and is a work of great originality. Much musicality lies in long passages of "word tennis," volleys such as "can dew and die can and die can tie."

Yet imagery was no less arresting for being more conventional, such as when philosophical answers are described as "an echo inside a shadow wrapped in cellophane."

Many of the opera's best effects don't make as strong an impression as they might with certain revisions. Certainly, the low-budget, barely adequate production directed by Frédéric Fisbach, notable mostly for its tacky cardboard cutouts, didn't serve the piece well: Without reading the program carefully, you'd be lost in the "shadows."

Even with improvements, the opera could be mistaken for a work of cerebral self-indulgence. In a world fraught with compromise, Shadowtime was built because it was possible. Whether or not there's an audience able to apprehend it, this stands with the best works of Milton Babbitt and Harrison Birtwistle as a monument to the constructive powers of the human mind. Luckily people still have that kind of self-belief.