The first difference is the antiphon and Psalms that are prayed at 1st Vespers for a 1st Class feast. In the Roman Breviary, at 1st Vespers, the Psalms are 143 (in two parts) and 144 (in three parts), with proper antiphon's before and after each Psalm. In the Dominican Breviary, a single proper antiphon is said before the first Psalm and after the last. This is referred to as the "super psalmos antiphon". The Psalms that are prayed are a special arrangement consisting of Psalms 112, 116, 145, 146, & 147. They are found on pages [1] and [2] of the Breviary, and are the so-called "laudate" Psalms, since they all begin with either laudate or lauda in the Latin. In his book "A History of the Dominican Liturgy", Fr. William Bonniwell, O.P., shows that the use of these Psalsm, with the single antiphon, goes back to the original codex of the Office by Humbert de Romans, and is one of the practices that the Dominicans carried over when they adopted the Office of the Roman Church (as opposed to some of the other, newer Offices that were being used in the mid-13th Century) as the Office of the Order. It was preserved in the Dominican Office right through the last revision in 1962.
There are a few exceptions (such as First Vespers of the Nativity of Our Lord Jesus Christ...which has five (5) antiphons to go with the five laudate Psalms), however, the single antiphon is generally the norm.
Some examples of the super psalmos antiphon for various feasts are as follows:
Feast of Our Holy Father St. Dominic
O happy parent, Spain, rejoice in giving to the world the joy of new offspring! But, rejoice still more, Bologna, because you are favored with the glory of so great a father. O universal Mother Church, sing in praise as you celebrate the festival of this new source of fame!
Feast of the Most Holy Trinity
O blessed, revered and glorious Trinity, Father, Son and Holy Spirit.
Feast of Our Lord Jesus Christ the King
He shall be a man of peace, and his throne shall be established forever.
Feast of All Saints of the Order of Preachers
The Lord raised up the needy from the dust and set them in the company of princes, and so, in the heavenly home, made Dominic the happy father of children.
The Octave Day of Christmas
What a wonderful exchange! The creator of the human race, taking to himself a living body, deigned to be born of a virgin; and becoming man, though without man for father, has bestowed divinity upon us.
Feast of St. Thomas Aquinas
The Blessed Thomas, Doctor of the Church, light of the world, glory of Italy, virgin shining with the bloom of chastity, rejoices in a twofold crown of glory.
Feast of St. Catherine of Siena
The virgin Catherine of Siena is to be extolled with undying praise, since the eminence of her sanctity has been made known to all mankind, alleluia.