Many Christians love Tolkien's fiction. Some love the books. Some love the movies. Some love both.
However, for some, this is a guilty pleasure. That's because C. S. Lewis is a Christian novelist in a way that Tolkien is not. Lewis uses thinly-veiled Christian symbolism and overt analogies.
As a result, some Tolkien fans resort to special pleading to make his fiction more Christian than it is. They offer typological interpretations.
Now in some cases I suppose that's more plausible. You could claim that Gandalf is a Christ-figure who dies for his friends, then is "resurrected." Mind you, that would be more plausible if Gandalf in general were more Christ-like.
i) I think one problem is when Christians feel the need to justifying their enjoyment of something that isn't Christian. But something can be good–artistically good–without being Christian. Even unbelievers must take their materials from God's hand.
ii) That said, I think there's a way of offering a more Christian interpretation of Tolkien. It seems to me that the genre is basically in the medieval chivalric tradition. Gandalf is priestly or monkish. Aragorn and Legolas are knightly. Saruman is an evil monk and sorcerer. Frodo is the holy fool. Gollum is an apostate. Sauron is a fallen angel. And medieval literature had mythological creatures which have their counterparts in Tolkien.