Complex sentence: In 1776 he completed his first opera seria "Didone abbandonata" after a libretto by Metastasio at the Teatro San Carlo in Naples by all accounts a great success.
Split into simpler sentences: In 1776 he completed his first opera seria "Didone abbandonata," after a libretto by Metastasio. It was given at the Teatro San Carlo in Naples and by all accounts a great success.