This is an absolute classic series and consistently makes all the best of children’s literature lists. Lewis wa a friend of J.R.R. Tolkien, who wrote another series based on a Christian allegory that you might have heard of, and both belong on everyone’s must read shelf. If you don’t want to pay attention to the underlying Christian message, it is still possible to read the series with enjoyment. I do agree with B.S that The Screwtape Letters is a very entertaining, ironic book which is worth reading, but it is also aimed at adults, not children, which must be taken into consideration in a comparison.