Just to show that it's possible to be critical and clear-eyed about C.S. Lewis without sounding like an idiot, check out Adam Gopnick's rather excellent article in this week's New Yorker. I particularly appreciate this paragraph:

Yet a central point of the Gospel story is that Jesus is not the lion of the faith but the lamb of God, while his other symbolic animal is, specifically, the lowly and bedraggled donkey. The moral force of the Christian story is that the lions are all on the other side. If we had, say, a donkey, a seemingly uninspiring animal from an obscure corner of Narnia, raised as an uncouth and low-caste beast of burden, rallying the mice and rats and weasels and vultures and all the other unclean animals, and then being killed by the lions in as humiliating a manner as possible—a donkey who reëmerges, to the shock even of his disciples and devotees, as the king of all creation—now, that would be a Christian allegory. A powerful lion, starting life at the top of the food chain, adored by all his subjects and filled with temporal power, killed by a despised evil witch for his power and then reborn to rule, is a Mithraic, not a Christian, myth.

Now that's criticism: a thoughtful, interesting observation that actually engages Lewis on his own terms. Is this sort of thing even allowed?