Delius' sympathy for his surroundings can be heard in his third opera, Koanga (C. F. Keary, after G. W. Cable, 1897), set on a Southern plantation; Appalachia (Trad., 1896, 1903), a series of variations on an American slave song; and the nocturne Paris (1899), in which a Straussian sumptuousness and vitality suggest interesting possibilities that Delius did not, in the event, pursue. Stylistic maturity came with his next opera, A Village Romeo and Juliet (Keary, after G. Keller, 1901), which, although marred at times by undistinguished vocal melody, culminates in the ecstatic "Walk to the Paradise Garden", after which the lovers scuttle the hay barge on which they are floating downstream. In Sea Drift (Whitman, 1904), for baritone, chorus and orchestra, poignant regret for love's transience is captured in music of ever-changing colour and chromatic flow as a boy sorrowingly observes a seabird whose mate never returns. More positive feelings are explored in the monumental A Mass of Life (1905), a setting of texts from Nietzsche's Also Sprach Zarathustra, Delius identifying himself with Zarathustra's philosophy of living life to the full and of developing courage in the face of approaching death.
The fortitude Delius had to muster as his health deteriorated was a contributory cause to a change in style in such works as the orchestral North Country Sketches (1914) and Eventyr (1917), where the sharper-defined sounds and uncompromising harmonies contrast with the sensuous sweetness of the earlier Brigg Fair (1907) and In a Summer Garden (1908). An unexpected turn to conventional forms in concertos for violin (1916), cello (1921) and violin and cello (1916) and sonatas for violin (1914) and cello (1916), marks, in general, a period of flagging inspiration, and by the 1920s Delius had become an invalid, paralyzed in both hands (1922) and blind (1925). Eric Fenby came to the rescue, and, acting as his amanuensis, helped Delius complete a final handful of works, most notably the Songs of Farewell (Whitman, 1930) for chorus and orchestra.