The Romantic Era took place during the 18th century in Europe, partly as a response to the Industrial Revolution. It focused on powerful emotions, which were heightened by the French Revolution and the Napoleonic Wars, and placed greater emphasis on older arts and customs.
During this time, Opera as art took new forms. The focus on old custom led to a focus on freedom (a direct response to Napoleon in the "rescue operas"), and the combined love and fear of nature. Enormous compositions were commonplace, with huge orchestral arrangements and the resurgence of Bel Canto (beautiful singing) as exemplified by the stereotypical Fat Tenors, who were chosen because their powerful lungs could sustain long and demanding passages in music. Emotion in the opera were taken to new heights, both to show the depth of the composer (and in reaction, the listener) and to give feelings of desire for dramatic stories in faraway places.
Another focus of opera was on folklore and supernatural activities in rural areas. Carl Weber's opera Der Freischütz (The Marksman) is considered the prototype of these operas. The love of larger-than-life tales and characters lent itself to operas based on Shakespeare, who enjoyed a resurgence in popularity.
The Romantic Era was a time of drastic change in the operatic movement, but one that allowed more freedom in music and song, and many of the Romantic operas are ingrained in culture as "typical" opera (Wagner's Ring Cycle, for example).