Hard to do that without making at a 'list of books that will induce a mindfuck and their spoilers'

It's hard, but I think not impossible. I was thinking mostly in terms of explaining to people who have already read the book why people believe it belongs there.

E.g. I love all of Douglas Adams' books, but I have no idea what they're doing on this list.

A non-spoilery hint at which concept in those books someone thought was a mindfuck, would be nice.