To get a couple of things out of the way: this is not the “definitive” recording of the Bach suites. I do not believe there can ever be such as a definitive rendition. However, it is very much worth having.
What makes this recording significant, is not that Casals got it “right” or was technically or musically better than today’s cellists. (Out of the 300+ recordings available at the moment, the top third probably match him for both qualities.) The big deal was the simple fact that, at a time when cellists concentrated almost single-mindedly on the Beethovenian and Romantic repertoire for their instrument, the most admired cellist in the world choose to perform these works in public, and then to record them. In doing so, Casals suddenly put them on the menu for a whole generation of cellists, and for their students (so that today any cellist trying to gain recognition feels they must record them – hence 300+ available titles).
The most striking aspect on first listen was that at least half of the 40 or so recordings I am familiar with seem to be strongly influenced by Casals. (In some cases, the decent thing would have been to include Casals as co-performer, since he is almost being copied.) As a rule, the more romantic the reading, the more it seems to owe to this rendition. Casals plays with verve, employing rubato for emphasis, but never excessively dramatizing. His reading is lighter than many modern ones, but opting neither for the emotional restraint nor the stress on rhythm so called historically informed performances strive for. The music doesn’t always flow freely, but appears as a series of statements (Rostropovich called his style “rhapsodic”.)
If today, 80 years after the recording was made, this is not one of the most memorable readings ever, that might be mainly for the reason stated above: there are so many openly romantic recordings by now, and most of them owe so much to this one, that it sounds almost overly familiar, even on first listen.
I was, and still am pleased with the sound quality. Not that it matched modern recordings, but the sound never keeps me from enjoying the music, either.
All in all, this is a recording anyone in love with these works should own for their historical significance. Anyone looking to own only one (or only a few) recordings, should first do their homework: listen to different performance styles, and make up your mind whether you appreciate historically informed, modern, deliberately idiosyncratic, or romantic readings. Only the latter would include Casals’ recording.