Opera seria
In the later part of the 18th century Christoph Willibald Gluck changed a lot of traditions in opera.  He did not want opera to be just a way for singers to show off their voices.  He wanted the story to be important.  He did not use dry recitative but tried to make the drama, dance and music all important, especially the chorus. Orfeo ed Euridice was his first important opera, followed by others such as  Alceste.