The other four are the Sequences of Easter, Victimae Pascali Laudes, of Pentecost, Veni Sancte Spiritus, of Corpus Christi, Lauda Sion Salvatorem, and All Souls, Dies Irae.
The Sequence is a hymn that is sung on particular feasts immediately before the Gospel. Taken with the long Tract of the First Sunday of Lent, the effect can be the heightening of expectation before the singing of the Gospel. However, the Sequence, unlike the Introit and the Gradual and Alleluia, seems to emphasise the text over the music. That is to say, there are generally fewer notes per syllable, making the Sequences resemble speech more closely. That would seem to indicate that the Church intended the text of the Sequence to be far more like a Lesson (a reading) than a Chant. It seems to me, therefore, that the faithful should give great attention to the Sequences, both as hymnody and as texts upon which to meditate.
In the first clip, the ladies from gloria.tv sing the usual chant version of Victimae Pascali Laudes. It is rhythmic and syllabic. It is also strophed, which is a common feature of the Sequences. That is to say, the melody of each line is repeated in the next. Compare this with the other four 'original' sequences.
The second clip has an irresistable energy to it that is not correct as a form of chant but, as liturgical music, does not depart very far from Gregorian Chant, while being a distinctive form. It certainly captures the victorious and triumphant theme of Easter.