“Papa” Haydn earned his sobriquet for his generousity with his students. But it could equally refer to his status as the Father of the Symphony and the Father of the String Quartet.
Haydn was already well-established when Mozart came on the scene; he died six decades later during his student Beethoven’s second period. In between, he wrote more than 100 symphonies–again, more than Mozart, Beethoven and Schubert, combined. And yes, some poor soul has ranked all of them:
https://www.classicfm.com/composers/haydn/guides/definitive-ranking-haydn-symphonies/
It is important to recall that Haydn’s orchestras were much closer to the proto-orchestras of the Baroque than the massive bands unleashed by Mahler at the dawn of the 20th century. Through these smaller orchestras, Haydn weaved compositions that became among the most sought after of the age. His fame oustripped Mozart’s. Schumann, Wagner and Brahms all held Haydn in great regard–perhaps more so than his now more celebrated contemporaries. I will confess: I don’t get it. Yes, we can hear the first strains of romantic sturm und drang in some of Haydn’s work. And his development of musical forms opened doors for his students to march through. He’s important–no question–but, in the end, not really for me.
Let his music provide the counterargument. Here are two of his best: the finale of his 49th (“The Passion”) and first movement of his 104th (“The London”).
Franz Joseph Haydn, Symphony No. 49 in F. Minor, “Passion”, IV. Finale, Presto:
Franz Joseph Haydn, Symphony No. 104 in D Major “The London”, I. Adagio-Allegro:
In 1795, Haydn abruptly stopped composing symphonies. Instead, he turned his larger scale ambitions to choral works–two massive oratorios and six masses would be completed before his death in 1809. It is entirely likely that Haydn’s late turn to choral music was inspired by his trip to London, one of his few foreign adventures, where he attended multiple performances of Handel’s works.
The first of these works was The Creation, a massive oratorio that reveived its first public performance in 1799. It is widely considered to be Haydn’s crowning achievement. Starting in Chaos, Haydn’s score works its way through the six days of Creation, followed by the emergence of Adam and Eve. Ever the happy optimist, Haydn ends the story there, with a chorus of praise for God–leaving Satan’s corruption, the explusion from Eden, and Abel’s murder for another day.
There is a lot to like here. Haydn amplifies the drama, especially with a massive C-major chord, delivered at maximum volume, to signifiy the creation of light (at 7:15 in the below). Haydn also uses unsettling harmonics to evoke emotional responses in his audience. But, perhaps the most important development here is how Haydn effectively uses music to convey through sound a world that is visual. Beethoven would attempt something similar in his Pastoral Symphony; Mendelssohn would master this technique some decades on.
Mozart remarked: “Haydn alone has the secret both of making me smile and touching my innermost soul.” Who am I to argue?
Franz Joseph Haydn, The Creation
A Gertus History of Music 