A love the full caster Bard because it is mythologically accurate. The word "bard" comes from reallife Celtic tradition, refering to a kind of mage. This mage did magic by means of formulating magical spells into words. Especially, the bard foresaw and manipulated the future by praising someone to bless them, and making fun of them to curse them. They are known for many other kinds of magic as well.
The famous Merlin is in fact a Celtic bard.
The slot 9 spell Shapechange allowing perpetual shapechanging into anything ultimately comes from a story about another Celtic bard, Taliesin.
The slot 9 spell Foresight is also a Celtic bard thing relating to the ability to foresee the future.
Power Word Kill is something the Celtic bard is famous for, where the satire litery deals body harm.
Generally, the main themes of the D&D class are prescience, healing, teleportation, shapechanging, and of course mind magic, of enchantment and illusion. These themes are mythologically correct.
I appreciate the accuracy because the term bard is a reallife term from a reallife culture. For the sake of cultural sensitivity, there is an ethical obligation to use the term in a reasonably appropriate way - and here D&D does this well.
The Bard class models Celtic magical traditions. But it turns out, the Bard class also describes Nordic magical tradions well. The healing, resurrecting, and protective magic relate to the Songs. The prescience relates to the Spa by the volva. Mind magic of enchantment and illusion relates to Seidr. The shapeshifting and teleportation relate to Form Travel.
The Celtic and Nordic traditions sometimes describe very powerful magic. The high level spellcasting of the Bard class is accurate too. The Bard is an important and excellent class.