Dear Revert 43,
I’ve copied the footnotes from the fisheaters site for comment and explanation of the “old” calendar versus the new. The actual cycles of the major feasts and times of the year are mostly unchanged from old to new. What is different is what they are called, plus the very great increase in Scripture which is included in the days in the new calendar: on a daily basis, First Reading, Psalm, Gospel; on Sundays (and Vigil mass on Saturday), First Reading (usually OT), Psalm, Second Reading (NT) and Gospel. My notes below are (attempted) in red.
Footnotes:
1 In the Novus Ordo:
the Seasons of Time After Epiphany and Septuagesima have been replaced by “Ordinary Time”; (True; same number of Sundays)
The Season of Time After Pentecost is referred to also as “Ordinary Time”; (True, and the Feast of Corpus Christi is added)
the Feast of the Circumcision is referred to as “Mary, Mother of God”;
Ascension Thursday is celebrated on “Ascension Sunday” (the 7th Sunday of Easter) in some provinces;
the Feast of Christ the King is not celebrated on the last Sunday of October but on the last Sunday in Pentecost, disrupting the relationship between Christ’s Kingship and the Triumph of the Saints celebrated on November 1 (All Saints Day), and leading to the idea that Christ doesn’t need to be recognized as King now, on earth, by all nations – but only after the Last Judgment will His Kingship matter; (This is really nit-picking; the actual dates of the feasts in both calendars are either on the same day, or within a week of each other)
some Saints’ Days have been removed from the Calendar (e.g., St. Christopher). Please know that this removal from the liturgical calendar doesn’t mean that the Saint in question has been “uncanonized,” “de-sainted,” or “demoted” as is commonly and frustratingly believed; (actually, Christopher and Valentine were somewhat “mythical” saints, in that there was little history to prove they actually existed)
some Feasts have been added; (Quite a few)
Ember Days have been done away with in most places;
Holy Days of Obligation in the United States are not celebrated if they fall on a Saturday or a Monday; (Not true; they are still celebrated, but the obligation to go to Mass has been removed; voluntary attendance is recommended)
the cycle of readings are not based on a yearly cycle but a three-year cycle Results: the entire rhythm of the liturgical year as it’s been known for millennia (actually, 400 years since Trent) is disrupted; though a greater quantity of Scripture is covered, it is a lower quality (?) of Scripture in that the new readings tend to omit mention of miracles, demons, Hell, evil, the sin of divorce, anything that offends Jews, etc. (This is just a simple exaggeration)
Regarding use of the monastic diurnal, there are multiple threads on CAF that seem to cover that subject more than I could hope to do. But, use of the diurnal would seem to be perfectly appropriate for your daily observation and prayers (with a sneak look at a modern parish calendar from time to time).
Hope this helps! Peace!