Kempff is always worth exploring in my opinion -- particularly in the late sonatas -- but Kempff does attract diametrically opposing opinions and I think you need to allow his interpretations to grow on you. His approach is to Beethoven is simplicity, lyricism, and inner power -- not everyone's view. Moravec's performance of Sonata 27 will reward your effort (Connoisseur Society label).
Late Beethoven Piano Sonatas
Love Schnabel's. I like Gieseking's Beethoven but I don't think it's quite the bullseye of Schnabel's. Would love to discover some others though. Kempff?