Metafiction is self-conscious about language, literary form, storytelling, and directly or indirectly draw attention to their status as artefacts
(From Wikipedia's description of metafiction.)
I'd say Lord of the Rings fulfills this.
Self consciousness about language:
Tolkien was a philologist. His thing was constructing languages. To begin with, each ...
Short of publicity stunts, there's not really anything clear-cut as to the differences. However, it's likely a publicity stunt due to this:
This is the MALE EDITION of the Dictionary. The FEMALE edition is almost identical. But NOT quite. Be warned that ONE paragraph is crucially different. The choice is yours.
This is the little paragraph on my copy of ...
There is one part in particular in The Two Towers where Frodo and Sam are discussing the story as a narrative that strikes me as metafictional in a way different than other comments have mentioned:
“I don’t like anything here at all,” said Frodo, “Step or stone, breath or bone. Earth, air and water all seem accursed. But so our path is laid.”