This piece is a part of a set of three pieces Debussy wrote for orchestra. "Nuages" means clouds, and Debussy portrays them by using a very soft texture - the orchestra doesn't play anything remotely harsh.
He also used parallel chords quite often in his music, and this piece is no exception. Therefore, I rarely felt like a cadence had been reached. My analysis may be incorrect, but one passage has this progression:
i VII i N VII vii(dim7)
This effect creates an undulating sound with little tension or relaxation, though the piece's minor mode does give it a somber feel overall. From the mood, I'd guess Debussy must have had gray, dreary clouds in mind when he wrote this piece. It sounds foreboding and very serious to me.
I read that the Debussy was influenced by a gamelan orchestra, and included a pentatonic melody in this piece as a result of that influence. If anything, it is a subtle reflection of gamelan at most. I've heard gamelan before, and a normal gamelan piece is very noisy and raucous - the instruments are all metallic and they're played with hammers. In "Nuages," the pentatonic melody is played softly by flute and harp.