Beethoven's last five string quartets were his final musical ideas and they were not particularly appreciated, or even understood, in his own time. He introduced many new and daring concepts including the expansion of the traditional four-movement form, unexpected harmonic relationships, and the use of a wide variety of tempo changes.
His original finale to the Opus 130 String Quartet is not the one that he used for publication. The finale that he first composed and premiered was the Grosse Fuge which he later withdrew and published as a separate entity, the Opus 133. It was apparently so challenging to his listeners that he actually wrote a different finale, a much lighter movement in a sonata-rondo form.
On this recording, the listener can choose to hear the revised ending of Opus 130 or the original finale (by skipping the revised ending and going directly to the Opus 133, the Grosse Fuge).