I'm clearly in the minority, among reviewers whose opinions I respect, in finding this performance unsatisfying. Let your own ears decide. The axiom is: It's only as good as it sounds.
The route from Bruges to Prague in the Renaissance, musically speaking, ran through northern Italy. What I mean is that the great Franco-Flemish composers first established their hegemony in the city states of Florence, Ferrara, and Venice, from whence their influence traveled north over the Brenner Pass into Hapsburgia. Heinrich Isaac was a major player in that transmission, working and establishing a huge reputation in Italy before becoming one of the dominant musical figures in the court of Maximilian. There's a persistent rumor about Isaac in Early Music circles, that he had a wife in every port - specifically in both Innsbruck and Florence. I can't verify it, but his simple part-song "Innsbruck Ich muss dich lassen" is one of the most beautiful and heart-felt compositions of all time. Isaac was a very fine composer by any standard - the peer of Josquin and Brumel in both skill and inspiration. It's a huge shame that he has not been very well represented on recordings. Among his magnificent liturgical compositions, there are only six available CDs of his masses, and only the rarest and most expensive is truly excellent. That one is the Missa Paschalis, sung by Ensemble Officium. The same mass is offered by the Schola Cantorum Stuttgart. Missa Virgo Prudentissima has been recorded by the Muenchner Dommusik; Missa Carminum by Capella Antiqua Muenchen; Missa La Spagna by ensemble Odhecaton; and a mass for Maximilian by ensemble Hofcapelle.
The Tallis Scholars' performance of Isaac's Missa de Apostolis has some virtues and many flaws. Its greatest virtue is that it makes Isaac available, sung at a fully professional level. Its flaws are stylistic. This judgement reflects my musical taste, and hey, de gustibus non disputandum!
The fourteen singers of the Tallis Scholars are all highly skilled musicians, with mature understanding of performance practice. So I suspect that my dissatisfaction with this and other recordings by the Scholars focuses on the musical decisions made by the conductor Peter Phillips. Phillips hears polyphony "from the top down." That is, he invariably overweights the superius (soprano) voice, at the expense of the lower voices, yet Renaissance polyphonists built their polyphony from the tenor outward, granting expressive independence to all voices. The "bottom up" nature of Renaissance polyphony is evident from the music itself in score, and from explicit statements by contemporary theorists like Glareanus and Agricola. Want to try an experiment? Put this CD in your system, then go into another room and listen. You'll hear the sopranos declaiming lustily over a muddle of bland male timbres.
Phillips achieves this top-line dominance by using women's voices on the superius, but men's voices on the alto, tenor and bass. I strongly suspect that he transposes some of the music he selects upward, to suit the strongest part of his sopranos' ranges. In any case, his sopranos always sing with full expressive technique, while the other voices tend to sing without expression or independence, a flat and somber affect. Expressiveness is good! But in this polyphonic realm it has to be distributed to the full ensemble. Remember, please, that the typical choir of Isaac's era had the most mature and developed singers among the tenors and basses, while the higher parts were usually sung by boys. Those boys must have been quite skilled, but it's hard to imagine that boys' voices ever dominated the music in the manner of Peter Phillips's sopranos.
Phillips is also a "one tempo" conductor, and that tempo is mournfully slow. Renaissance theoreticians suggested that the "tactus" (the counting beat) of polyphony might be found from the pulse of the conductor; Phillips clearly has a pulse of about forty beats per minute. Not only is his tactus slow, but it's also monotonous. There's no reason, either historically or by way of the modern listener's ears, to justify such ponderous interpretations.
As I declared at the beginning of this review, many listeners may fiercely disagree with me, may find the strong soprano timbres thrilling, may consider the use of male countertenors in place of women's voices distasteful. All I can do is to suggest comparing the results. Listen to any Tallis Scholars CD in your collection, and then listen to a piece of similar music sung by The Clerks Group, or the Orlando Consort, or the Ensemble Gilles Binchois, or the Binchois Consort. If you still prefer the Tallis Scholars, well, ITA MISSA EST.
Added much later: a comment I've just received prompted me to listen to this performance again. I've decided that I set the bar too high and I've upgraded my rating by a star. I don't want to retract my criticisms of the Tallis Scholars here; what I wrote still seems appropriate. But sometimes I have to overlook my own expectations and just be grateful for the performance as it is. The Missa de Apostolis is a gorgeous composition, and this recording is the best we're likely ever to have a chance to hear.
I think I was too harsh in my critique of the "Hofkappele" ensemble's recording of music for Maximilian, also. They sing better, on the whole than the Tallis Scholars. They deserve another listening. But the really 'hot' vocal ensemble, performing music of Isaac's era, is Cinquecento. Get any one of their recordings, listen to it before and after one by the Tallis Scholars. I swear you'll hear the difference.