It is absolutely correct to say that the Constitution on the Sacred Liturgy said, abundantly, that the reform of the Liturgy should above all seek to engage the People of God in active participation. Examples of this exact sentiment in the document abound. The Council Fathers were well aware that in the decades before the Council, the ordinary way of attending Mass was "hearing" a spoken Mass, often enough with responses provided by the servers. They were evidently concerned that people must not only pray at Mass, but must pray the Mass....Is it really the case that you are going to knock the principle of 'full, conscious, and active participation?' This full participation should be "exalted" above all else! Read the Constitution on the Sacred Liturgy again, friends, and tell me that this principle of participation is not primary. It is not the "easy road." It is THE road that the Constitution lines out. And then to knock it in favor of "beauty?" Is not the sound of a full throated assembly singing a "beautiful" thing? Do you think it is an ugly sound? And it keeps coming: "above prayer." Are you saying that when the gathered assembly is participating, it is not prayer? Hello....
Therefore, David is right to say that participation was the highest principle governing the reform. However, it is incorrect to suggest that participation--at least participation of a certain type--is the highest principle governing the liturgy. Participation is a richer concept than mere activity, and the Liturgy is a richer concept than participation.
Since the Council, our liturgical context has changed quite dramatically. Participation in one sense is at an all-time high. Almost every Sunday Ordinary Form Mass now contains congregational singing (although not many would qualify as sung Masses). Responses are always said by the people, and never, in my experience of the Ordinary Form, by servers alone. Lay people distributing Communion regularly outnumber the ordinary ministers. "Active" participation in this sense is no longer a problem. Reform in this sense has now succeeded. The mandate of the Council, in this sense and this style of active participation, has been accomplished--and then some. Or rather, it will be accomplished once some of the excesses have faded away (hopefully with the same weary inattention that caused the demise of felt banners), and once the dialogues of the priest and people have received their rightful attention.
However, the work of fostering FULL, CONSCIOUS participation has hardly begun. How can it possibly begin, until congregations are made aware of and have an opportunity to sing all of the texts that pertain to them? The people are regularly denied any contact whatsoever with some of the antiphons--the proper antiphons--that SC said they had a right to in paragraph 30, the paragraph which is the intradocumental touchstone of congregational participation. (Note that the paragraph did not say that the people must sing motets.)
And how can FULL, CONSCIOUS participation be achieved until the music that cantillates the Ordinary of the Mass heightens the words, instead of obscuring them?
And how can FULL, CONSCIOUS participation be achieved when the celebration of Sunday Mass is in most places said in a hurried and casual way, full of distractions, and with consistent disregard for the precepts of the Church? The Council Fathers rather insisted "that the faithful come to [the Liturgy] with proper dispositions, that their minds should be attuned to their voices, and that they should cooperate with divine grace lest they receive it in vain."
According to the Council, the Sacred Liturgy "is an exercise of the priestly office of Jesus Christ, Head and members," and to the extent to which the members are not engaged in the work of their own salvation, they are not participating in the Liturgy. It is almost completely inadequate to just show up and sing along with whatever song is being offered. There is an interior work to be done, and the post-Conciliar reform has barely begun to address this.