My greatest disappointment was not hearing Kempff live. I had tickets for a Sunday afternoon recital he was due to give at London's Royal Festival Hall late in his career, and it was only after taking our seats I discovered he had cancelled: we heard Shura Cherkassky instead. He was good - but I so wanted to hear Kempff!
These recordings were made over 4 years in the pianists late 60's/early 70's. The technique is still good - though there is the occasional splash [as in the last movement of D.784]. But their chief value is that Kempff allows us to hear Schubert as his friends must have heard him when he first played them in private. There is nothing at all flashy about the performances, no concert-hall projection, just intimate music making that gets to the heart of these elusive scores. Here we get 18 of the 21 sonatas which survive either complete or as fragments. Missing are sonatas #7 - D.567, #9 - D.571 with D.640 and D.570 i&ii, and #11 - D.613. Those unfinished by the composer are left as torsos, without any moderate [Badura Skoda] or radical [Tirimo] re-constructions and conjectural completions.
There are pianists who play these works with greater [often misplaced] bravura: but none, I suggest, who get to the heart of the music with such directness and selfless simplicity. These are performances to hear and hear again; and they warm the heart as few others can.
Edit: In a recent survey of all available recordings of Schubert's last sonata [D960] for 'Gramophone' magazine, Bryce Morrison chose Kempff's recording as the finest of all. [Kempff, incidentally, includes the first movement exposition repeat which many pianists omit.]