His music contains dissonance, chord progressions that don't resolve, expressing his intent to create musical moments that are are fleeting and veiled as the paintings of Monet and other Impressionists. For him, music was made up of tonal colors, a sense of fluidity and atmospheric effect. Because of his interest in exploring tone color to produce shimmering musical beauty, he retreats from any percussive intensity that might intrude on the senses.
His musicians "ear" turned away from traditional sounds as he heard music from Asia. The Gamelan orchestra that performed at the Exposition in Paris in 1889 produced harmonies out of the pentatonic (five note)scale, sounding much different from the do-re-mi-fa-sol-la-ti-do Major/Minor scales of Western harmonies. Debussy, whose music is gently beautiful, opened a new vista of musical language for composers who would become the grand iconoclasts of the 20th Century.
Where's the beat?
You cannot dance to his music. He avoids a regularly occuring pulse that you can tap your foot to, spreading a rhythm over such a wide expanse of music you will hardly be able to follow it.
His music is intentionally "vague," with a melting quality from one section to the next, so that all of the architectural structure is hidden. He obscures the skeleton to focus attention on the shimmering sound.
Listen to a moment of Real Audio file from his composition "La Mer." Click link. At the website click on 20th Century, scroll down and click on "Debussy," then click on "La Mer" in the text. Listen to a moment from La Mer by Debussy