I'm firmly with the majority on this one. I love the disc and agree that it's beautiful and thorougly uplifting. Perhaps I've just got cloth ears, but I can't hear any of the dodgy tuning complained of by another reviewer here, and (WARNING - sacrilege approaching!) I much prefer this version of Victoria's Missa O quam gloriosum to that of the Westminster Cathedral Choir, which has never moved me in the same way.
The tracks from the Codex Calixtinus and Libre Vermell are truly lovely, and the polyphonic motets by Lassus, Victoria and Clemens non Papa are exquisitely paced, pitched and sung, in my view. And there is a heart-stoppingly beautiful version of Mouton's Nesciens mater. It's a fabulous disc.
In addition, in the notes there's a very perceptive introduction by Gardiner and a scholarly but approachable analysis by the excellent Tess Knighton. It's a tad over-packaged for my taste, but that's a tiny quibble. Gardiner has fully earned his high reputation and this disc does that reputation full justice. Not to be missed.