The Narnia series was written for children, and there's nothing better than reading them aloud. I read all seven, seven times over to my sons as they were growing up. They feed the imagination of moral right and heroism.
The Tolkien trilogy was written for adults. Quite hard to read aloud: the sentences and paragraphs are a lot more complex, and the pace isn't brisk enough or the language bright enough to carry children along. These are adult epics, steeped in an overall tragic sense, blood-bought by a very hidden Christ.
That's certainly a fair point, but even when I read them as a child I recall thinking, "Yes, Aslan is Christ, I get it."
It seems a bit clumsy and heavy-handed.