One reason C. S. Lewis's criticism is so good is that he has such a great sense of humor, and he wields it as a weapon against his critical opponents. I love these two paragraphs from his Preface to Paradise Lost:

We must therefore turn a deaf ear to Professor Saurat when he invites us to 'study what there is of lasting originality in Milton's thought and especially to disentangle from theological rubbish the permanent and human interest' (Milton, p. 111). This is like asking us to study Hamlet after the revenge code has been removed, or centipedes when free of their irrelevant legs, or Gothic architecture without the pointed arches. Milton's thought, when purged of its theology, does not exist. Our plan must be very different--to plunge right into the 'rubbish,' to see the world as if we believed it, and then, while we still hold that position in our imagination, to see what sort of poem results.

In order to take no unfair advantage I should warn the reader that I myself am a Christian, and that some (by no means all) of the things which the atheist reader must 'try to feel as if he believed' I actually, in cold prose, do believe. But for the student of Milton my Christianity is an advantage. What would you not give to have a real, live Epicurean at your elbow while reading Lucretius?