The magnitude of this collection cannot be overstated. Beethoven wrote his 32 mature piano sonatas between 1795 and 1822. Although they were never meant as a complete collection, they are very meaningful in understanding his whole body of works. That makes them according to pianist and influential critic Hans van Bülow The New Testament of piano literature.
Just like his string quartets, Beethovens oeuvre for piano sonata can be divided into three periods: early, middle and an extremely difficult to play late period. The early period sonatas were inspired by Haydn and Mozart, the middle period found Beethoven trying to find his way, finally growing into such complicated work that it took fifteen years before Liszt was able to play them all for the first time.
Although the entire box consisting of twelve records is quite something to go through, it contains some real beauties. A bit dated in performance perhaps, but certainly still a high quality recording. I found this a joy to listen to.