The Screwtape Letters didn't scare me, but I only read them when I was grown up. Catholic propaganda.
That Hideous Strength was interesting, but I was coming out of childhood and Catholicism and could see where the writer was going.
I haven't read any of his books but my children loved The Lion the Witch and the Wardrobe and they were, and are, seemingly unaware of any religious references.
His house - where he spent his last years - is very near to where I live and there is a lovely little Nature Reserve - made out of his garden and land - adjoining. He is buried in the local C of E churchyard and there is a beautiful Narnia window in the church near to where he always used to sit.