Haydn is very different from Beethoven and so comparisons there are difficult. Of course anytime we make such comparisons we must remember that if we use the values of one era or style as the standard measure it will certainly result in a skewed comparison. For example, if we compare Rembrandt to Matisse the comparison will surely not be fair if the standards we use are those of Rembrandt's era (anatomical accuracy in drawing, realism, the illusion of three-dimensional form). By the same token, Rembrandt might look rather "dull" by the standards of Modernism: his use of color is tame, he's not incredibly inventive in form, etc...
Haydn was one of the two central figures of the Classical era along with Mozart. Mozart was undoubtedly the greater composer and his early death was one of the greatest losses of Western music. Having said this much, Haydn still stands as one of the towering figures of classical music... not far beneath the "Three Immortals": Bach, Beethoven, and Mozart. Classicism in music was sandwiched between the Baroque and the Romantic eras... both of which were far more about virtuosity. Classicism distilled, codified, or "simplified" musical forms so that the listener could virtually grasp the whole of a work in his or her mind. Perhaps one might think of how we can grasp a sonnet in the same manner... how it sets up certain expectations and limitations... but how these may result in the most masterfully original results in the hands of the best poets.
Admittedly, this era is one of the most challenging for many listeners... especially those familiar with the more blatantly outgoing music of the Romantic and Post-Romantic era which in many ways still dominates the airwaves of classical radio and stands as the established vocabulary of most film music. Where the Baroque has Bach, Vivaldi, Handel, Biber, Telemann, and several other composers well-known to aficionados of the era, and Romanticism has an endless array of "greats" (Schumann, Schubert, Chopin, Wagner, Brahms, Bruckner, late Beethoven, Richard Strauss, Mahler, etc...) the Classical era is often imagined as divided solely between Mozart and Haydn. In a way, the classical era strikes me as not unlike the classicism of 18th century poets who are often quite ignored and underrated in comparison with the later Romantics... but these composers... including Haydn... certainly grow upon the listener who is willing to put forth the effort.
Haydn can also be initially difficult to appreciate as a result of the immense scale of his oeuvre which makes it challenging to know where to begin. Beethoven wrote but 9 symphonies; Mozart wrote 41... but generally it is only no.s 25, 29, and the final 6 or so that are considered among his mature and greatest works. Haydn wrote 104 symphonies!! His final collection of symphonies, known as the "London Symphonies", which include many of his finest works, in comprised of 12 symphonies which push beyond some of the ideas of Mozart. Beyond these there are the 6 "Paris Symphonies", and any number of works from his middle years which are included among those known as his "Sturm und Drang" Symphonies. Add to this his endless string quartets, piano sonatas, choral works, operas... and one may well be overwhelmed... especially when the works remain firmly footed within the given classical structures so that it takes several hearings to begin to discern the differences or the original elements that are so obvious in the works of the Romantic composers such as Beethoven.
The symphonies are full of magnificent moments... and as a whole reward repeated listening. Listen to the muscular start of symphony no. 98 which stands as a precursor to the brooding works of Beethoven. I like this particular rendering... which captures the muscularity of the opening of this work... and because of the discussion by the conductor who admits to his own youthful doubts about Haydn in a brief pre-concert talk:
http://www.youtube.com/watch?v=GUlEBoqHYK8
Of course there's the magnificent 104th:
http://www.youtube.com/watch?v=90t9w7aLZL0
The closing to this symphony reminds me of one of Beethoven's more joyous passages... such as the peasant dance from his 6th (Pastoral) Symphony:
http://www.youtube.com/watch?v=JVHVRLQ79K0
And of course there's this playful symphonic exploration of a simple theme and variation:
http://www.youtube.com/watch?v=ZJDWh9F3Vig
Of course this but scratches the surface of Haydn's symphonic output... and his symphonies may not be his greatest achievement. Haydn was quite literally the inventor of the string quartet... and an unsurpassed master of the form. What Haydn achieved in the quartet was something of a democratic art form. Rather than the concerto in which a single virtuoso instruments dominates the dialog, as it were, with the string quartet Haydn virtually created a musical equivalent of a dialog... in which four instruments/speakers take turns talking, arguing, laughing, etc...:
Here is the famous adagio cantabile from the Emperor Quartet:
http://www.youtube.com/watch?v=Rc34Jr9udlU
And a few other marvelous selections:
http://www.youtube.com/watch?v=KS_TF...eature=related
http://www.youtube.com/watch?v=hymdXgFND4I
Of course, being a fanatic of vocal and choral music, I might just suggest that Haydn's choral works are his most towering achievements. Haydn quite well surpasses both Mozart and Beethoven as a choral composer. Among his great choral achievements: St. Cecilia Mass:
http://www.youtube.com/watch?v=LmixN...eature=related
http://www.youtube.com/watch?v=-uqw37PwVYA
The Lord Nelson Mass:
http://www.youtube.com/watch?v=2E9Iu...eature=related
and Haydn's nearly undisputed masterpiece, The Creation... an oratorio that clearly builds upon Handel... and vies with Handel's Messiah as one of the greatest oratorios ever composed:
http://www.youtube.com/watch?v=Q5RHDwdaanQ
http://www.youtube.com/watch?v=Vafm_PdWsrI
http://www.youtube.com/watch?v=3Yg6PMCkmJc
