Adam C. Zern shares his thoughts on C.S. Lewis's Mere Christianity:
"C.S. Lewis is of course most well-known for his Chronicles of Narnia series. I think far more compelling, however, are his commentaries on Christian theology, which include extra-scriptural explications on everything from psychology to sociology. Thus far I have read two of Lewis's commentaries, The Four Loves and now Mere Christianity. I liked them both equally, but I had a unique reaction to various aspects of Mere Christianity.
I don't think it would be inappropriate to label a large portion of Mere Christianity as brilliant, even inspired. His writings on human nature, the Second Coming of Jesus Christ, the personality and historicity of Christ, and his logical connections, his prose, and his analogies are truly thought-provoking. The first three quarters of the book are well-worth a recommendation for others to read the book.
However, and I realize the criticisms that follow are totally subjective and based on personal theological disagreements, the last quarter of the book kind of fell off of a cliff for me. In my opinion, not even C.S. Lewis, even with all his brilliance and insight, can make the doctrine of the Trinity make any sense at all; although, I will admit that he has come closer than any other Christian I have spoken with or read. Lewis becomes more of a logician than theologian (which he wouldn't claim to be anyway) toward the end of the book, working himself into logical pretzels that became, in my mind, somewhat nonsensical.
Mere Christianity is a great book, definitely worth reading. Even if you have doctrinal disagreements with Lewis, which I certainly had, there is plenty to ponder in this relatively short book. Lewis gave more reasons than not to continue to read his other writings. I genuinely want to know what he thought, and I can't say that about many authors."