I've never read his non-fiction. I like the Father Brown stories, they're fun, but they are also full of plot holes and retrofitted explanations, and the characters are pretty thin. I feel a bit the same about C. S. Lewis. His non-fiction is brilliant, I love The Inner Ring [1], but his stories don't really have depth. I think it's not surprising that 2 out of the 3 I mentioned had their greatest success with children's books.

[1] https://www.lewissociety.org/innerring/

I don't really enjoy the fiction of C. S. Lewis at all, really, and even G. K. Chesterton's fiction is not that good, it feels very contrived and it feels like preaching to the choir. As part of the choir there is a lot I agree with, but I don't quite get the point of his fiction.

But Chesterton's non-fiction books, The Everlasting Man, Orthodoxy, What's Wrong With the World and Heretics are some of the best and most insightful books I have ever read, and they really took me by surprise because I did not expect them to be what they are. They are full of speculation, and misunderstandings, but they are also full of very deep insights into humanity.

I do, however, think the fiction of Tolkien is historic and unsurpassed, nothing written since really comes close IMO.

Which CS Lewis fiction have you read? Till We Have Faces is the best IMO and few people seem to read it. I also like Out of The Silent Planet and That Hideous Strength, although not the middle book of that trilogy, Perelandra. The Screwtape Letters and The Great Divorce are pretty good too.

I am not sure Tolkien's books are accurately described as children's books. The Hobbit perhaps, but not the Lord of The Rings IMO.