What is the mood of the story of Orpheus?
The greatest difficulty with this question is that it is not obvious which version of the story you are referring to. The myth of Orpheus and Eurydice appears in many versions, including in Virgil's Georgics, Ovid's Metamorphoses, and the Orphic Hymns. Musical versions include Monteverdi's L'Orfeo and operas by Gluck and Haydn, an operetta by Offenbach, as well as a ballet with music by Stravinsky, and several twentieth-century stories, poems, and musical retellings. The mood varies, depending on the particular version of the story.
Since the basic narrative of this legend involves the death of Orpheus' wife, Orpheus' journey to the underworld to bring her back to the world of the living, his second loss of her due to his looking back, and his eventual death at the hands of the Thracian women, one can say that the general mood is unhappy, punctuated by a brief moment of joy when Orpheus thinks Eurydice will be able to follow him back to the world of the living, immediately followed by despair when this hope proves false.
The mood of the the story of Orpheus and Eurydice is certainly sad (as the above post stated), but I would say that the mood is more ominous. Even before the story, Hymen, who came to the the wedding of Orpheus and Eurydice, gave a prophecy that stated that their marriage would not last. Starting from this point the tone is ominous. We can say that the reader is on alert for something bad to happen.
As the story progresses, Eurydice is in the fields wandering. When Aristaeus, a shepherd, sees her beauty, he chases her. She escapes but is bitten by a snake and immediately dies.
When Orpheus finds out about it, he weeps in song. These songs are so powerful that they even melt the hard heart of Hades, who allows Orpheus to fetch Eurydice from the underworld. The one condition is that he must not look back at her during the assent.
The reader remembering the prophecy of Hymen knows and feels that the story will not end well, and the story does not end well, as Orpheus looks back and loses his love forever.
The mood of Orpheus, The Great Musician retold by Olivia Coolidge is sorrowful. Orpheus loses his lover. She dies, but he thinks he can get her back only to be disappointed again. Finally the resolution of the story occurs when Orpheus is killed while singing about his deceased lover Eurydice. The women of Thrace killed Orpheus because they were infuriated by Orpheus's contempt. The whole story is filled with sadness and Orpheus seems to spread his sadness to normally happy people.