One of those listed has, as a central belief, the teaching that "As man now is, God once was. As God now is, man shall become." I think this qualifies as a false gospel. And I feel fully qualified to call it such. More examples could be cited.
I have read much CS Lewis, but not recently, and I cannot claim to be a Lewis scholar. He is a superb apologist for the Christian faith, in my opinion. (He even defended the idea of purgatory.) I am currently re reading the fiction of JRR Tolkien, very close friend of Lewis, and instrumental in bringing Lewis to Christ. Tolkien was a robust Catholic.
Please don't overlook Francis Schaeffer, either. He deals more directly with the role of Christianity in a post-modern world than does Lewis, and is just as easy a read. I would recommend his Trilogy for starters.