Most notoriously, the word song is changed to chant - and chant clearly distinguished from a hymn (see 86) - and new conditions are added for the option not to sing the actual proper of the Mass: anything that replaces a proper chant or a seasonal proper chant must also be "suited to the sacred action, the day, or the time of year."
Paul Ford has very helpfully marked up a huge file to compare the versions side by side, and highlight the portions that apply to music in red. Here is the link.
Here is a comparison of the old and new text as it concerns the Introit, and the same changes affect the Offertory and Communion.
OLD
In the dioceses of the United States of America there are four options for the Entrance Chant: (1) the antiphon from the Roman Missal or the Psalm from the Roman Gradual as set to music there or in another musical setting; (2) the seasonal antiphon and Psalm of the Simple Gradual; (3) a song from another collection of psalms and antiphons, approved by the Conference of Bishops or the Diocesan Bishop, including psalms arranged in responsorial or metrical forms; (4) a suitable liturgical song similarly approved by the Conference of Bishops or the Diocesan Bishop.
NEW
In the Dioceses of the United States of America, there are four options for the Entrance Chant: (1) the antiphon from the Missal or the antiphon with its Psalm from the Graduale Romanum, as set to music there or in another setting; (2) the antiphon and Psalm of the Graduale Simplex for the liturgical time; (3) a chant from another collection of Psalms and antiphons, approved by the Conference of Bishops or the Diocesan Bishop, including Psalms arranged in responsorial or metrical forms; (4) another liturgical chant that is suited to the sacred action, the day, or the time of year, similarly approved by the Conference of Bishops or the Diocesan Bishop.
It is easy enough to predict that this will have no immediate effect on what takes place in your local parish. Legislation can never really force a change as a substantial as a shift from singing hymns to singing the Mass itself. However, it can make a difference over time, as the permission to replace liturgical texts with non-liturgical texts becomes ever more restricted and narrow.
