An article on Mozart by Terry Teachout is well worth your time. He makes one of those points which is so frustratingly obvious in retrospect:

To my mind, no one has done a better job of concisely explaining what makes Mozart Mozart than Donald Tovey, whose essay on the G Minor Symphony, K. 550, the greatest of the minor-key works, is a convenient starting point. Tovey offers a seeming paradox that will startle many readers: “We can only belittle and vulgarize our ideas of Mozart by trying to construe him as a tragic artist.” What could he possibly mean, especially with reference to the G Minor Symphony, still widely regarded as the locus classicus of tragedy in music? The answer, Tovey replies, is that Mozart was up to something altogether different: “Mozart’s whole musical language is, and remains throughout, the language of comic opera.”

This bald-faced assertion, so surprising at first glance, turns out on closer inspection to be all but self-evident. From the rush and bustle of the outer movements of the G Minor Symphony (whose compositional language Tovey likens to Rossini’s Overture to The Barber of Seville) to the wittily “theatrical” exchanges between soloist and orchestra in the later piano concertos, one finds in Mozart’s mature instrumental works an abundance of proof that he thought of all his music in dramatic terms—and that the kind of “drama” he had in mind was 18th-century opera buffa, abstracted at times to the point of sublimity but still essentially comic.

For the Romantic of deepest hue, such a claim must necessarily have the effect of trivializing Mozart’s minor-key music. But Mozart himself, lest we forget, was not a Romantic—indeed, Romanticism per se did not exist in his lifetime—and thus was not afflicted by the paralyzing idea that comedy is unserious.