Are his characters faithful? Christian! Do his characters sacrifice? Christian! It's ridiculous.
It's also a bit of cheat for Spengler to dismiss both Eliot in The Wasteland and Frazer in The Golden Bough by writing:
Frazer attempts to show that all Christian imagery and ritual derive from pagan myth, for example, the commonplace idea of a sacrificed god. His conclusions have been rejected by later scholars, but the relevant point regarding Eliot is that he embraced the pagan antecedents of Christianity as he thought it was (even though it turned out to be something else than he thought).
Oh really? Which later scholars would those be? Christian scholars? Frazer's work has been revised and historical inaccuracies have been corrected, but I am unaware of anyone who would argue that Christian imagery and ritual are sui generis or unique. Easter eggs anyone? Christmas trees anyone?
No, in the grand pagan tradition of Beowulf, The Iliad, and The Odyssey, Tolkien tells stories of decline and loss. His worlds are those where the Gods withdraw, and the age of Heroes comes to an end. Power is dangerous and life is tragic. Even the ludic, immortal Elves must accept Necessitas, the inescapable nature of fate. If Christianity replaces the pagan world, then Christianity is another word for domesticity and mortal life. A definition I have yet to ever come across.
More importantly there is no Gospel. Just the tale of there and back again. And Frodo is not sacrificed so much as transformed by experience. He does not transcend in his departure from Middle-Earth so much as signal the end of an age. The new age is only possible when he is gone, and that age belongs not to Jesus but to Sam.
Sam returns home to marry, become mayor, and enjoy long years with his family. He is much more like a comical sidekick version of Odysseus returned to Ithaca and Penelope than an apostle.
And like Joyce in Finnegans Wake or Calasso in The Marriage of Cadmus and Harmony, we read a new version of Vico's cyclical history: The Divine Age gives way to the Heroic Age, and the Heroic Age gives way to the Civic Age. In the end we no longer have the gods, but we have their stories in the form of myth and legend. We may no longer be capable of heroic deeds, but we are capable of writing great literature.
And that was Professor Tolkien's real contribution and achievement: not Christian apologetics, but a beautiful story in the pagan tradition.