Ahh pianostreet, the flat earthers of classical music taste.
I've studied and analysed the Beethoven piano sonatas in detail for ~22 years. I have heard recordings by ~60 different pianists, including ~17-18 complete cycles. I have graduate and postgraduate degrees in music. It is my carefully considered opinion that Arrau's Beethoven is lousy, with the exception of the following recordings:
Op. 57, Ascona, 1959 [Aura/Ermitage]
Op. 10/3, Brescia, 1973 [Music & Arts]
Op. 53 and 81a, Columbia Studios, 1947/49 [United Archives]
All of which are good, if perhaps not the last word in any of these sonatas.
Arrau's best recording, and one everyone should hear, is the recital of 20 May 1963 in Lugano, where he plays Brahms's Variations on a Theme of Handel & Ravel's Gaspard de la Nuit. The rest of the 1959 Ascona recital from which the Appassionata I recommended above comes is also worth hearing: Schumann's Fantasy and Debussy's Pour le piano (plus Chopin's C-sharp minor Etude). And I have always been fond of his 1964 Tanglewood recital of Mozart piano sonatas, even though it is not exactly in a style suitable to Mozart. In general, most live recordings by Arrau are worth hearing.
His
studio Beethoven recordings, however, including both complete cycles, can safely be avoided. Most of the later live recordings (including the other ones packaged with the Brescia Op. 10/3 I mentioned) are also not very interesting; his attempts at the late sonatas were always soporific. There are many better choices: Paul Badura-Skoda, Olga Pashchenko and Peter Serkin on period instruments; Schnabel, Annie Fischer, Edwin Fischer (no relation), Bruce Hungerford, Friedrich Gulda, Hisako Kawamura, Jörg Demus, Michel Dalberto, Michaël Lévinas, Mitsuko Uchida, Steven Osborne, Solomon Cutner, Stephen Kovacevich, etc, on modern instruments. For people who really like slow, relaxing, easy-listening, Beethoven for babies type performances, Wilhelm Backhaus, Emil Gilels and Grigory Sokolov do so with much better command of piano touch and sonority than Arrau ever had.
I would accept praise of Arrau's studio recordings if one were discussing, say, his recordings of Schubert D946, D760 & D780 from 1956 on EMI, or the set of Schumann's major piano works he recorded from 1966 to 1976 for Philips, or for that matter the even later set of Chopin's major piano works recorded from 1973 to 1984, all of which do reveal a musician with deep insights into the Romantic repertoire and an innate understanding of the music of Schumann in particular, equalled by few others. But the technical ability with which he backed up these insights has been surpassed by many others before and since; and the studio tended to rob him of the energy of live performance that otherwise allowed him to overcome these deficits. And his Beethoven happens to just... not be good most of the time. It and the studio Mozart sonatas are the weakest part of his discography, and I have to assume the high praise he (and Barenboim, and Brendel; and for that matter Karajan, Thielemann, etc) has always received for his Beethoven is because most critics do not actually like the music of Beethoven very much and wish his music had been written by Ludovico Einaudi instead.