These sonatas are among the finest keyboard productions of the late-classical era. More intimate than Beethoven's, yet imbued with more rhythmic pulse than Mozart's, they require much taste and restraint from the performer. They're also relatively lengthy (the briefest in this set runs nearly 30 minutes). Consequently they're not very popular showpieces for professional pianists, while amateurs rarely develop to the point of being able to play them well. Ironically, Schubert's sonatas are highly melodic and ingratiating, dramatic without being overbearing, sentimental but not maudlin -- just the sort of music that should be "popular."
Brendel's performances are, to these ears, very convincing. He structures each of these episodic pieces brilliantly, rendering a coherent and affecting musical statement. For all its alleged waywardness, there is a transcendent sort of continuity in the music that defies analysis, expressive of a certain though mysterious moment in the composer's life; to hear the transition from classicism to Romanticism, one might listen to Schubert's late sonatas. If that seems too much like "homework," consider that, for melodic invention, Schubert is second to no one who ever presumed to write music.