Man's Magnum Opus. What is the greatest work of art in any medium?

The Calling of Saint Matthew
1599-1600
Oil on canvas
10' 7 1/2" X 11' 2"
Contarelli Chapel, Church of San Luigi dei Francesi, Rome

Ok, in the spirit of our afternoon agreement on engineering exclusions I wonder if concepts and fields of study should be excluded as well? Should stuff like mathematical algorithms count?

I think you have here illustrated the difficulty of establishing an answer to your question.

The work is massive and spans the entire wall behind the altar of the Sistine Chapel. It was executed from 1537 to 1541. The Last Judgment is a depiction of the second coming of Christ and the apocalypse. The souls of humans rise and descend to their fates, as judged by Christ surrounded by his saints.
The Last Judgment was an object of a heavy dispute between Cardinal Carafa and Michelangelo: the artist was accused of immorality and intolerable obscenity, having depicted naked figures, with genitals in evidence, inside the most important church of Christianity, so a censorship campaign (known as the "Fig-Leaf Campaign") was organized by Carafa and Monsignor Sernini (Mantua's ambassador) to remove the frescoes. When the Pope's own Master of Ceremonies, Biagio da Cesena, said "it was mostly disgraceful that in so sacred a place there should have been depicted all those nude figures, exposing themselves so shamefully," and that it was no work for a papal chapel but rather "for the public baths and taverns," Michelangelo worked the Cesena's semblance into the scene as Minos, judge of the underworld (far bottom-right corner of the painting) with Donkey ears {i.e.foolishness} while his nudity is covered by a coiled snake. It is said that when Cesena complained to the Pope, the pontiff responded that his jurisdiction did not extend to hell, so the portrait would have to remain.

Even Poe has done some things better - how about the first and last stanzas of Israfel (the middle stanzas bring it down however).

You just brought me a realization: I prefer "melodic" (heavily rhythmic, emphasis on rhyming, and much smoother flow) poetry just like I prefer melodic music. My favorites of his after The Raven are Alone (I empathize greatly with some of the opening lines) and Annabel Lee (and it's soaring last stanza).