A response to Fr. Kocik's post.
One of the biggest liturgical shifts following the council was the breakdown of clear lines between the High Mass (everything audible sung) and Low Mass (nothing sung). Like many of the things that came as a part of the council's liturgical reforms, I think they may have been meant well, but in practice, has failed spectacularly.
I understand the concept of what it intended to do. In theory, it would enable a parish to have more liturgical singing, for example, a priest singing all the dialogues and his prayers, even if a choir or cantor could not be present. Or it could allow a congregation to chant the ordinary (in addition to the priest chanting his parts), even if a cantor capable of chanting propers could not be present. It would allow the Sung Mass model (that is, the ideal) to be more widely used, in situations where it would have been otherwise impractical or impossible in the Extraordinary Form, where a sung Mass cannot be celebrated without a cantor capable of chanting the propers of the Mass. In other words, Progressive Solemnity should enable Masses to be generally celebrated in a more ideal manner, bringing things higher and closer to the ideal of a sung liturgy.
However, it has had the exact opposite effect in almost every case. Instead of allowing priests to bring things closer to the ideal and to sing more, it lead to a widespread laziness where singing the actual Mass itself has become quite a rare thing. The allowance to sing every prayer or a minimal number of prayers has caused most priests to sing very minimally (if they follow the rubrics) or even none (if they ignore them), effectively annihilating the sung Mass from use in most parishes. Human nature being what it is, we often need rules to keep us on the straight and narrow.
Was progressive solemnity a good idea to try? I think so. Was it successful in enabling more singing? Absolutely not.