To my not-very-well-trained ear, almost all composers before Debussy sound a little dated, corny, and constrained, and most composers after him - Bartok and Messiaen being important exceptions! - sound abstract and unmusical.

Debussy's music is at this equilibrium point where the harmonic language is complex and atonal enough to evoke a spectrum of iridescent colours and haunting, ambiguous moods inaccessible to traditional common-practice harmony, but just constrained enough to avoid the descent into hostility and noise.