Pianist and author Charles Rosen on Beethoven:
Beethoven enlarged the limits of the classical style beyond all previous conceptions, but he never changed its essential structure or abandoned it, as did the composers who followed him. In the other fundamental aspects of his musical language, as well as in the key relations within a single movement, Beethoven may be said to have remained within the classical framework, even while using it in startlingly radical and original ways
This recording is myself playing Beethoven's hauntingly sad - but calming - Moonlight Sonata.
If you're interested in listening to some other Beethoven Sonatas there are some excellent recordings available on the Piano Society.