To the best of my knowledge, this Telefunken "Das Alte Werke" set was the first ever integral recording of the Bach cantatas. It is not the first complete recording, that was Rilling, but Rilling never set out with the intention to record them all, it sort of developed that way. As a result, the gap between the first and last Rilling recordings is more than 20 years, and the later recordings, although performed on modern instruments and with women's voices, were informed by the growing knowledge of period practice. The "Das Alte Werke" set was the first set to seek a unified approach, and in addition to try to recapture the sort of sound that would have been more like the sound Bach would have heard, using copies of the instruments that he would have known.
I have not heard all of these cantatas, but I know many of them from the initial LP releases I have in my collection, in their nice brown boxes (2 LPs per box) with miniature scores and detailed booklets. I enjoyed them, but, in my opinion, they have been surpassed. Nicky and Gus were trailblazers in the business of "authentic" performance (insofar as actual authentic performance is possible), and they of course suffer from the fact that people who follow reap the benefit of lessons learned and take things one step further. The use of these instruments was in its infancy and the orchestral sound is often thin and scrawny, the intonation of the valveless natural horns and trumpets often insecure. And occasionally I was caused to wonder whether some of these recordings had been made in Nicky's garden shed. In the now nearly 40 years that has followed, new generations of players have made these instruments their own. The Gardiners, Suzukis, Herreweghes and Koopmans have advanced the art and their orchestras sound much better than the orchestras in these works.
In the interests of "authenticity", the "Das Alte Werke" recordings eschewed women singers, opting to go with boy sopranos and counter-tenors. Bach would naturally have used all-male singers. However, boys' voices broke much later in Bach's time, so Nicky and Gus are actually trying to reproduce a sound that no longer exists, indeed that no longer CAN exist. Having said that, the quality of the singing is generally very good, and some of the boy soloists (from various boy's choirs, including the Vienna Boys' Choir and the King's College Cambridge choir) are really quite amazing (e.g., the opening solo of BWV28). The contributions of the grown-up soloists are also often outstanding (Max von Edmond and Paul Esswood come particularly to mind).
Having said all that, and acknowledging that this is a monumental achievement of the recording industry, I know enough about this set not to want to buy it, because to me the Gardiner/Suzuki sets sound so much better. However, I know people who absolutely adore this set, and who like the feeling of "insecurity", of operating slightly on the edge, of the whole thing, because this is what Bach must have been used to, considering he often had only a week to write, rehearse and perform a new cantata. These folk are the natural customers for this set. For anyone else, before splashing out this much money, I'd advise getting a single set of the cantatas (I believe the two-LP sets were released in CD form) and listen to one, to see whether you like the approach and the sound - and of course comparing with the likes of Gardiner and Suzuki, not to mention the older recordings of Richter, Werner and Rilling. Here's a good place to get a sample of "the big two", BWV140 and 147:
http://www.amazon.co.uk/Bach-JS-Sacred-Cantatas-BWV/dp/B0043IZ4VA/ref=sr_1_cc_1?ie=UTF8&qid=1292763940&sr=1-1-catcorr
One of the enormous (and to me enormously irritating) conceits of this set when it first appeared was the statement, more or less in so many words, that this was the only way to play Bach, and that any other approach was wrong. Hopefully, this has been erased from the record by now. This is music for eternity and should be played to the full extent of its artistic and aesthetic possibilities, not strapped in a stylistic straitjacket, using women's voices and modern instruments, if need be. I still turn to the old Erato Werner recording of BWV140 and the glory of the three trumpeting Läubin brothers blowing up a storm in Rilling's BWV129. Bach performance is not set in stone, nor should it be.