The song is SO simple, really serving to emphasize the beauty of the dusk. The gentle turns in the vocal line sound like the world settling in for the night, much like the lilies, the ladybirds, and the lovers that the text mentions.
And from answers.com:
This, from Massenet’s collection Poème pastoral, is one of his most delicate and understated songs, with, in the hands of the right performers, a haunting effect as insubstantial as the twilight that it describes.
The accompaniment is almost completely in the treble, and consists largely of light, quick arpeggios, separated by extended rests. The vocal part, with frequent chromaticisms, is equally understated, without any wide intervals, changes in dynamics, or even a distinctive melodic line.
Massenet later orchestrated it under the same title, for string orchestra and flute, violin, and cello. ~ Anne Feeney, Rovi