The Roman Canon had been untouched since the 7th Century
For those unfamiliar with the Traditionalist movement (and even those who think they know Traditional Catholics), the common accusation applied to the Traditionalist is being a man too attached to earthly traditions. The Traditionalist is a modern day Pharisee. He cares for beautiful vestments, golden chalices, and ritual but he cares little (or at least less) for his neighbor and for the poor. He is viewed as an enemy of the authentic teachings of Christ and is personified in the story of the rich man (cf. Matthew 19:16-26 ) and in the parable of the two men who enter the temple to pray (cf. Luke 18:9-14).
Yet, this straw man depiction of the Traditionalist is entirely off point. The Traditionalist’s end goal is not found in ornate vestments or mysterious rituals. The Traditionalist is concerned with giving to God the utmost glory and the first of all things (cf Matthew 6:33). And as such, our Lord is deserving of the most ornate of vestments and the most opulent of chalices. It is not the Traditionalist – no! – it is the Lord to whom the honor is given.
Even those familiar with the Traditional Movement, but those who are not traditionalists, will at least know of the Traditionalist’s arguments against the changes in the Liturgy. They will have heard the Traditionalist lament the omission of kneeling in the Nicene Creed; the change of “pro multis” to “for all”; and the changes in the Rites of Confirmation, Ordination, and the Eucharist.
Yet few people realize – and few Traditionalists lament as loudly as they do the aforementioned issues – the grave consequences of introducing multiple canons into the Holy Liturgy.
Since all time the Roman Canon had be recited by the priest silently. The priest – in imitation of Moses – ascends to a place where the Faithful cannot venture. It is in this holy place – at the altar of God – where the priest confects the Holy Eucharist and offers to the Eternal Father the Precious Blood of His Divine and Only Son, our Lord Jesus Christ, the 2nd Person of the Blessed Trinity. This is a task of the priest alone to accomplish – the people present can offer nothing other than marvel at the mystery.
Silence is not a foreign concept to Catholics. Catholics should be familiar with the story of Elijah who heard God in the small whisper:
And he said to him: Go forth, and stand upon the mount before the Lord: and behold the Lord passeth, and a great and strong wind before the Lord over throwing the mountains, and breaking the rocks in pieces: the Lord is not in the wind, and after the wind an earthquake: the Lord is not in the earthquake. And after the earthquake a fire: the Lord is not in the fire, and after the fire a whistling of a gentle air.And when Elias heard it, he covered his face with his mantle, and coming forth stood in the entering in of the cave, and behold a voice unto him, saying: What dost thou here, Elias? And he answered. (1 Kings 19:11-13)
Yet the Novus Ordo brought about four Eucharistic Prayers recited in the vernacular and recited loudly. Gone was the sense of mystery. Gone was the priest entering the holy place to pray for the people. The Novus Ordo Liturgy has succumbed to the vision of Martin Luther - the priest is no longer seen as an alter Christus.
The Canon is an ancient prayer. It is for Catholics the prayer of utmost importance in the Liturgy since it is by the prayers of the Canon that the greatest miracle in the world takes place on the altar.
Since the seventh century [the Traditional] Canon has remained unchanged. It is to St. Gregory I (590-604) the great organiser of all the Roman Liturgy, that tradition ascribes its final revision and arrangement. (Catholic Encyclopedia)
In the Ambrosian Rite, during the Canon the priest will stretch out his arms in the shape of a Cross
Yet, despite the sacredness of the Canon, the aftermath of the Second Vatican Council saw the elimination of one unified Canon and the creation of multiple canons. In fact, even in our world today, priests freely use their own ad lib words during the Canon and potentially (if not always) invalidate the Sacrifice of the Mass upon the altar. This is for the Traditionalist a grave and utmost serious situation.
In the 1970 and 1975 Latin editions of the Roman Missal, there are four Eucharistic Prayers (these may be augmented in the third editio typica which is due out this fall). In more recent American editions of the Roman Missal, in addition to the four already mentioned, there are five others included in the appendix: two for Reconciliation and three for Masses with children. Thus for the last twenty-five years, the Roman rite has had the experience of many Eucharistic Prayers.
This was not always so, however. For some 1600 years previously, the Roman rite knew only one Eucharistic Prayer: the Roman canon.
In the average parish today, Eucharistic Prayer II is the one most frequently used, even on Sunday. Eucharistic Prayer III is also used quite often, especially on Sundays and feast days. The fourth Eucharistic prayer is hardly ever used; in part because it is long, in part because in some places in the U.S. it has been unofficially banned because of its frequent use of the word "man". The first Eucharistic Prayer, the Roman canon, which had been used exclusively in the Roman rite for well over a millennium and a half, nowadays is used almost never. As an Italian liturgical scholar puts it: "its use today is so minimal as to be statistically irrelevant".
This is a radical change in the Roman liturgy. Why aren't more people aware of the enormity of this change? Perhaps since the canon used to be said silently, its contents and merits were known to priests, to be sure, but not to most of the laity. Hence when the Eucharistic Prayer began to be said aloud in the vernacular, with four to choose from -- and the Roman canon chosen rarely, if ever -- the average layman did not realize that 1600 years of tradition had suddenly vanished like a lost civilization, leaving few traces behind, and those of interest only to archaeologists and tourists.
(Source: From One Eucharistic Prayer to Many: How it Happened and Why by Father Cassian Folsom, O.S.B)
What serious theological implications does this have for a Catholic?
In the Eucharistic Prayers, moreover, the repeated petitions to God that He accept the Sacrifice have also been suppressed; thus, there is no longer any clear distinction between Divine and human sacrifice.
In Eucharistic Prayer IV the Church--as One, Holy, Catholic, and Apostolic--is abased by eliminating the Roman Canon's petition for all orthodox believers who keep the Catholic and Apostolic faith. These are now merely all who seek you with a sincere heart. The Memento of the Dead in the Canon, moreover, is offered not as before for those who are gone before us with the sign of faith, but merely for those who have died in the peace of Christ. To this group--with further detriment to the notion of the Church's unity and visibility--Eucharistic Prayer IV adds the great crowd of "all the dead whose faith is known to You alone." None of the three new Eucharistic Prayers, moreover, alludes to a suffering state for those who have died; none allows the priest to make special Mementos for the dead. All this necessarily undermines faith in the propitiatory and redemptive nature of the sacrifice.
In the Preface for Eucharistic Prayer II--and this is unprecedented--the various angelic hierarchies have disappeared. Also suppressed, in the third prayer of the old Canon, is the memory of the holy Pontiffs and Martyrs on whom the Church in Rome was founded; without a doubt, these were the saints who handed down the apostolic tradition finally completed under Pope St. Gregory as the Roman Mass.
Chapter VII The Alienation of the Orthodox
The Apostolic Constitution explicitly mentions the riches of piety and doctrine the Novus Ordo supposedly borrows from the Eastern Churches. But the result is so removed from, and indeed opposed to the spirit of the Eastern liturgies that it can only leave the faithful in those rites revolted and horrified. What do these ecumenical borrowings amount to? Basically, to introducing multiple texts for the Eucharistic Prayer (the anaphora)--none of which approaches their Eastern counterparts' complexity or beauty--and to permitting Communion Under Both Species and the use of deacons. Against this, the New Order of Mass appears to have been deliberately shorn of every element where the Roman liturgy came closest to the Eastern Rites.  At the same time, by abandoning its unmistakable and immemorial Roman character, the Novus Ordo cast off what was spiritually precious of its own. In place of this are elements which bring the new rite closer to certain Protestant liturgies, not even those closest to Catholicism. At the same time, these new elements degrade the Roman liturgy and further alienate it from the East, as did the reforms which preceded the Novus Ordo. In compensation, the new liturgy will delight all those groups hovering on the verge of apostasy who, during a spiritual crisis without precedent, now wreak havoc in the Church by poisoning Her organism and by undermining Her unity in doctrine, worship, morals and discipline.
Taken from The Ottaviani Intervention by Cardinal Ottaviani
And so the Traditional must fight on – not concerned at the slanders used against him. Men may accuse him of “intolerance,” “lack of charity,” or “exaggerated concern with the externals,” but the Traditionalist will fight on so that in all the Masses of the world the Holy Eucharist may be lawfully confected and offered to the Eternal Father in the most fitting, righteous, and worthy manner possible.
In the bull Quo Primum Pope St. Pius V declared: "By this present Constitution, which will be valid henceforth, now, and forever, We order and enjoin that nothing must be added to Our recently published Missal, nothing omitted from it, nor anything whatsoever be changed within it." And he concluded: "No one whosoever is permitted to alter this notice of Our permission, statute, ordinance, command, precept, grant, indult, declaration, will, decree, and prohibition. Should anyone dare to contravene it, let him know that he will incur the wrath of Almighty God and of the Blessed Apostles Peter and Paul."