The first Sunday of Advent marked the fiftieth anniversary of the introduction of the Novus Ordo Mass, and there have been many reports on the internet and elsewhere reporting the anniversary. However, I have not seen anything from anyone with first hand experience of the changes.
I remember my experience of the day, and I have to say that for me it certainly was not a major event. I was a student at the time at Liverpool University, and although I attended Mass every Sunday and often during the week, I was completely unaware that a major to the liturgy was planned. I think very few people did. I cannot recall any announcement beforehand, and even if there had been, I doubt whether I would have taken a lot of notice, because there had been so many changes over the preceding years.
On the day, I attended Mass in a parish church close to where I was living. I recall that two leaflets were handed out in stead of the usual one. It had been the practice in most churches that cards or booklets were handed out on which were printed the Ordinary of the Mass in its 1965 form (or the latest revision of the 1965 form). In those days almost everyone carried their own missal, so until the Novus Ordo was introduced, these could be used for the propers, which had not changed - at least not significantly. On the first Sunday of Advent 1969, a second leaflet was handed out including the new propers. The only really noticeable difference was the inclusion of an Old Testament reading.
The changes on that day seemed minor compared with those that had been introduced over the preceding five years. If I recall correctly, these included the use of English, the abolition of the Prayers at the Foot of the Altar, the abolition of the Last Gospel, the use of lay people as readers and much more.
Looking back, the most notable thing was the complete absence, at least in my case, f any form of explanation of the changes. For example, it took me about four years to discover that the Sunday readings followed a three yearly cycle; and about a further ten to find out that the weekday Masses followed a different cycle.