For classic Lutheran theology, hymns are a theological "source:" not up there with Scripture, of course, but ranking not-so-far below Luther's "Small Catechism." Hymns, in this tradition, are not liturgical filler. Hymns are distinct forms of confessing the Church's faith. Old school Lutherans take their hymns very seriously.
Most Catholics don't. Instead, we settle for hymns musically indistinguishable from "Les Mis" and hymns of saccharine textual sentimentality. Moreover, some hymn texts in today's Catholic "worship resources" are, to put it bluntly, heretical. Yet Catholics once knew how to write great hymns; and there are great hymns to be borrowed, with gratitude, from Anglican, Lutheran, and other Christian sources. There being a finite amount of material that can fit into a hymnal, however, the first thing to do is clean the stables of today's hymnals.
Thus, with tongue only half in cheek, I propose the Index Canticorum Prohibitorum, the "Index of Forbidden Hymns." Herewith, some examples.
Go check out the rest of what he has to say here