1. Mascagni was a verismo composer
Mascagni became world famous for his Cavalleria rusticana, an opera based on the short story with the same title by Giovanni Verga. He was labeled a "verismo" composer, and to this day is largely incorrectly regarded as such.
At the time Mascagni chose the subject of Cavalleria, Verga was already a well-established Italian author. His short stories were written in a style closely building on the French naturalist movement, in particular the works of Emile Zola. Italians called that movement "verismo" in the 1870s. As Maria Nockin puts it:
"Verismo," or realism, a movement which began long before in France, had already made significant contributions to the renewal of literary prose by adding new areas of subject matter, including everyday life events occurring to ordinary people. Instead of elevated rhetoric, accurate and frank description became the norm. As it progressed as a literary genre and metamorphosed into "Naturalism," the lives of lower class and underworld characters were included, introducing a note of the sensational. In Italy the "Verismo Movement" culminated in the development of more flexible and realistic dialogue, regional settings and considerable local color. As a result the works of the late nineteenth century helped regenerate the then stagnant Italian theater.
The definition of operatic verismo remains more controversial, but in the case of Cavalleria at the very least consists in basing the libretto of the opera on a verismo story.
Looking at Mascagni's fourteen operas that premiered after Cavalleria rusticana, one doesn't find many pieces that deserve the label of "verismo". Those who do without much doubt are Silvano and Amica. Some operas have hints of verismo, like Lodoletta or I Rantzau. All in all, this is a fairly weak case for an all-verismo composer.
What should be noted is that Mascagni's intentions were never to become a verismo composer, or to remain one after the success of Cavalleria. What is very often misunderstood is that Mascagni had extremely high artistic ideals. Before starting work on Cavalleria, he had been a starving musician touring with operetta companies. His letters from the time suggest that he may have been close to a depressive state at times. His only goal was to complete his first opera, his dear Guglielmo Ratcliff, an ambitious work started in the early to mid-1880s. He realized himself, and was also advised by friends, that Ratcliff, a difficult work, would be almost impossible to stage as a first opera. So when the Sonzogno contest (who eventually won him the first prize and international acclaim) was announced, it was seen as a ray of hope for Mascagni that could allow him to get out of his misery. He decided to start work on Cavalleria rusticana as what we would qualify today as a "commercial" work: a work which would conquer audiences, even if that meant making a sacrifice of some of the ideals Mascagni had developed in Ratcliff.
Cavalleria rusticana became the success we know and turned out to be a masterpiece. Mascagni liked all his operas, and certainly liked Cavalleria very much would never cease to like it until his death.
What is more interesting is looking at how far away from verismo Mascagni went compared to some of his collegues. In fact, it has been reproached to Mascagni that many of his operas were not very dramatic. This should not be necessarily understood in the sense that he failed at creating verismo works, but rather that those operas simply did not intend to be dramatic in the same way Cavalleria or La Boheme did.
Consider Guglielmo Ratcliff, Mascagni's first and lifelong favorite opera. The text put into music comes directly from the Italian translation of Heinrich Heine's play. The play's first and second acts consist entirely of narration. The third act has some action. The last act is almost entirely narrative as well. Consider the whole of Zanetto; the last act of Iris; and finally, Parisina, an over four hour-long opera consisting mainly of dialog and narration.
Those operas tell you that Mascagni was not so much inspired by the actual drama happening on stage, than by the beauty of the text.