The Ceremonial of Bishops sets the context in no. 297:
With this Mass, celebrated in the evening of the Thursday in Holy Week, the Church begins the sacred Easter Triduum and devotes herself to the remembrance of the Last Supper. At the super on the night he was betrayed, the Lord Jesus, loving those who were his own in the world even to the end, offered his Body and Blood to the Father under the appearance of bread and wine, gave them to the apostles to eat and drink, then enjoined the apostles and their successors in the priesthood to offer them in turn.
This Mass is, first of all, the memorial of the institution of the eucharist, that is, of the Memorial of the Lord's Passover, by which under sacramental signs he perpetuated among us the sacrifice of the New Law. The Mass of the Lord's Supper is also the memorial of the institution of the priesthood, by which Christ's mission and sacrifice are perpetuated in the world. In addition, this Mass is the memorial of that love by which the Lord loved us even to death.
The rubrics, by way of exception, allow for the local Ordinary to permit another Mass in churches and oratories to be celebrated in the evening, and, in the case of genuine necessity, even in the morning. Such Masses are provided for those who are in no way able to participate in the evening Mass and not for the advantage of individuals or (newly added) special small groups (Roman Missal, rubrics for the Evening Mass of the Lord's Supper [EM], no. 3).
The rubrics then make a mention of the liturgical decoration. "The altar may be decorated with flowers with a moderation that accords with the character of this day" (EM, no. 5).
The Church bells are rung during the singing of the Gloria and then remain silent unless "if appropriate, the Diocesan Bishop has decided otherwise" (EM, no. 7).
The decision about this matter no longer involves the conference of bishops. A further musical specification is provided: "the organ and other musical instruments may be used only so as to support the singing" (EM, no. 7).
The rubric following the washing of the feet is more descriptive than the presently existing one: "After the Washing of Feet, the Priest washes and dries his hands, puts the chasuble back on, and returns to the chair, and from there he directs the Universal Prayer. The Creed is not said" (EM, no. 13).
In a new rubric it is noted, "At an appropriate moment during Communion, the Priest entrusts the Eucharist from the table of the altar to Deacons or acolytes or other extraordinary ministers, so that afterwards it may be brought to the sick who are to receive Holy Communion at home" (EM, no. 33). This may require that parishes do some preliminary planning for this to successfully happen.
It is explicitly stated that the Prayer after Communion is said by the priest "standing at the chair" (EM, no. 35).
The order of procession is more carefully described for the transfer of the Blessed Sacrament to the place of reposition. Newly added is the description : "A lay minister with a cross, standing between two other ministers with lighted candles leads off… Before the Priest carrying the Blessed Sacrament comes the thurifer with a smoking thurible" (EM, no. 38).
The directions for what the priest should do once he reaches the place of reposition have been supplemented. "[T]he Priest, with the help of the Deacon if necessary, places the ciborium in the tabernacle, the door of which remains open" (EM, no. 39). He then incenses the Blessed Sacrament while Tantum Ergo Sacramentum or another Eucharistic song is sung. Then the "Deacon or the Priest himself places the Sacrament in the tabernacle and closes the door" (EM, no. 39).
The previous Roman Missal (Sacramentary) seemed to indicate that the stripping of the altar followed immediately, whereas the current Roman Missal notes, "At an appropriate time" the altar is stripped (EM, no. 41).
The faithful are "invited" in the Roman Missal to spend time in adoration (EM, no. 43). It was formerly indicated that the faithful "should be encouraged."
A totally new rubric is found at the end of Holy Thursday. "If the celebration of the Passion of the Lord on the following Friday does not take place in the same church, the Mass is concluded in the usual way and the Blessed Sacrament is placed in the tabernacle" (EM, no. 44).