This beautiful rendition of the Kyrie, Gloria and Credo is taken from the renowned "Missa de Angelis" (Mass VIII) of the Kyriale. Solemn, gracious, peaceful, edifying...always in my heart.
It's fine for academic Latinists, philologists, and etymologists, but not so much for a reformed Catholic who believes in the Common Tongue for worship. This chant imparting peace, relaxation, and calm of mind is fine, just so long as it stays out of official worship - where it has the capacity to become just peaceful, relaxing, and calming at the expense of true reasonable worship in the heart. Sorry, I'm obliged - by my membership in the Anal Retentive Reformed Papist Society - to find something to complain about. Beautiful none-the-less. My novus ordo Catholic Basilica often sang the Kyrie (then went straight to a Marty Haugen Gloria, go figure).
I don't see any reason why, for instance, the Kyrie can't be sung just like it is. Any Christian familiar with the liturgy knows what Kyrie Eleison means, it's not detrimental to anything. That being said, the ordinary of the mass can be sung in the vernacular with the gregorian melodies.