This work, D 956, is truly superb. It's one of the best chamber pieces ever written. I prefer it to anything written by Beethoven. How come you aren't too familiar? It's a standard, a real classic. The second movement in particular is fantastic. In the 20 months after Beethoven's death, Schubert went on a composing frenzy partly because he knew that his days were numbered (he died Nov 1828) and partly out of reverence to Beethoven. Just about everything Schubert wrote in this period is a stunner. D 956 was among the very last pieces composed.