Can't disagree with any of this!
Good hymns focus on God -- theocentric and theological song, addressing God and invoking Him as Trinity, Pure Perfection, and First Cause of creation.
Good hymns use words and themes from Scripture or Tradition -- Every good hymn doubles as a Bible lesson, or as an encapsulation of some patristic or otherwise traditional theme. Its author looks for inspiration to the Gospels or Psalms, or to the Church's spiritual legacy.
Good hymns treat transcendent concepts -- A good hymn, like good spirituality or theology, is marked by a tension between heaven and earth, by a both/and character that is at once richly temporal and richly eternal. Often it moves thematically from creation to heaven, from earthly to eschatological
Good hymns employ sacred diction -- hymns with sacred diction directly enhance our participation in the Sacrifice of the Mass by reminding us that, for a time, we have left the ordinary world behind, and entered into a holy presence where common words are inadequate.
One of the things that should be mentioned, is to not confuse a hymn with a song. Minor technical point, but a hymn is verse after verse. I’m not sure that the “bad” literature that so many people dislike falls into that category.