The above review was nearly enough to put me off this, but I'm really glad it didn't. The reviewer has taken an extremely puritan stance to how it should sound, which, considering the paucity of information handed down, seams rather fanciful to have such clear-sightedness as to the particulars, but he may well be a scholar of the period who knows a thing or two I don't. As to his "positive organ" comment, it is barely used and used very carefully.
The singing is immaculate and the recording very fine. This contains probably my favourite recording of Perotin/Perotinus, although the Dessoff Choirs record, though rougher, is also a favourite. Though never made digitally available, it can be found here http://188.8.131.52/1/items/lp-00592_BeG/
Recorded in 1976, the notes would imply that David Munrow's interpretations of this music were somehow revolutionary in massively reducing the instrumental accompaniment compared to previous thinking as to how these works would have been performed. I hate to think what those earlier performances were like, as there is more than enough instrumentation to be heard here.
Even in the organum pieces, Leonin's "Viderunt omnes" and his three other works here are attended by bells, plus Perotin's own version of "Viderunt" as well as "Sederunt principes" by positive organ. The motets of the ars antiqua are performed with the mindset that everything must be accompanied by some mentalist walloping away like mad on the tabor and a cacophony of other instruments. The ars nova motets on the second disc fare a little better with instances of unaccompanied or subtly accompanied pieces, but there are still some examples of overblown instrumentation to be found there too.
Full Latin/Old French sung texts are supplied with English translations (and although there are no modern French translations, an Old French - Modern French glossary is given). The notes say virtually nothing about the music itself but are more concerned with telling us what a wonderful wonderful guy David Munrow was.
Groundbreaking in its day? That's as maybe, but there have been so many better recordings of Notre Dame, ars antiqua & ars nova music since this.