Johann Sebastian Bach is perhaps the most-transcribed of all major composers. The reasons are obvious: his music is immensely satisfying for musicians to study and learn and is not generally sensitive to changes in tone color.
The first issue in judging a performance using a transcription is the aptness of the performer's choice. In this case, there is little reason to object. The viola is the instrument closest to the cello, the one is tuned exactly an octave higher than the other. Fingering and bowing technique are a little different, but violists rarely have trouble playing a cello part an octave up and in fact the music is a little easier because the distance between notes on the strings is less. As a matter of fact, there are authorities -- including Baroque cellist Anner Bylsma -- who think the cello suites might have been written originally on viola. We don't know for sure because Bach's manuscript is lost.
Barbara Westphal is a leading German violist, and has chosen to play the suites on a modern viola. (Modern in terms of its technical set-up; the instrument itself is a Gaspar da Salo made in 1570, at least 150 years before the composer wrote the music.)
The performance is technically completely secure, with a firm, singing tone (minimal vibrato, thankfully) and an obvious awareness of recent discoveries concerning proper style. It does not quite have the depth of interpretation of the top three or four cello versions known to this writer, which might be a function of the fact that the violist has to struggle a bit less to play the notes. Nevertheless, it is a first-rate interpretation that should reward repeated listening, and is a must for viola fanciers. Fine natural sound can be attributed to the production and engineering team of Seiler/Schalloran.