How did Christoph Willibald Gluck’s reform operas differ from traditional opera seria?

Christoph Willibald Gluck’s reform operas were a direct reaction against the excesses of traditional Italian opera seria, which he and his collaborators viewed as hindered by predictable structures and unnecessary artifice.1

Key differences included:

• Subordination of Music to Poetry: Gluck championed the principle that the true office of music is to serve poetry, rejecting the florid, ornamental da capo arias that often interrupted the dramatic flow.1
• Simplicity and Truth: He replaced elaborate vocal displays with a "beautiful simplicity" and naturalness of expression, aiming to restore opera to its function as a drama set to music.1
• Integrated Structure: Unlike the rigid alternation of recitative and aria in opera seria, Gluck’s works utilized orchestrally accompanied recitative to smooth transitions and gave greater importance to ensembles and choruses.1
• Dramatic Cohesion: Influenced by Enlightenment ideals and the work of Jean-Georges Noverre, Gluck’s operas—such as Orfeo ed Euridice—prioritized emotional truth and dramatic continuity over the display of solo coloratura.12