Anyone who knows me much knows I love C. S. Lewis. I read a Narnia book as a very young pagan, and read some of Mere Christianity shortly before my conversion. Lewis' now-popularized Lord/Liar/Lunatic argument was very troubling to me as a young cultist, and the Holy Spirit used that towards my conversion to Christ.
I've read Narnia to my kids, quoted Lewis in many connections in my sermons, writings, here and at Pyro. His Screwtape Letters have done me a lot of good (particularly Letter 8).
Lewis is wonderfully articulate. When he says something well, it can't be topped. You can just quote, nod, marvel, and wish you had half his eloquence.
But I've never had any illusions about the fact that Lewis was doctrinally problematic at best. He has to be read with a lot of discernment. Lewis was wobbly or just plain wrong on some very important issues (inspiration of the Bible and atonement being two of them).
Views of Lewis have ranged from nutty rejection as a witch (seriously) to unquestioning acceptance and citation as a theological authority. Which he's not.
All that to say this: Gary E. Gilley has written about the best brief and even-handed assessment of Lewis I've ever seen (h-t Old Truth). I commend it to you.