Satie was a torchbearer for the avant-garde. Described by his contemporaries Ravel and Debussy as a "precursor"-- a label that fits perfectly given how much he came to influence composers and artists like John Cage and Man Ray.
Satie did not fit in his time, and he does not fit in ours. The preference for "easy on the ear" music persists, and for good reason.
We intuitively respond to melody and harmony, to music with narrative-like structure and stirring emotional content. We so often come to music for exactly these qualities: to be liberated from thinking and give ourselves over to feeling.
Satie understood this, and his genius in his most famous pieces was to make music that appealed to both the intellect and the emotions, not slighting one in favor of other.
Gymnopedie No. 1 and Gnossienne No. 1 make this point vividly. These delicate, abstract, short pieces may have reached the level of pop classics, but our familiarity with them masks how revolutionary they were.
The invented names Gymnopedies and Gnossiennes signal that Satie is inventing new forms of music, mostly without time signatures or bar divisions, and with some very esoteric sources of inspiration. Their haunting, wistful qualities are evoked as much by the absence of musical convention as by the presence of pleasingly melodic lines and chords.