Conversation so far:
What types of books did Michael Crichton read?
What did Michael Crichton write?
He wrote, among other works, The Andromeda Strain, The Great Train Robbery, Congo, Sphere, Jurassic Park, Rising Sun, Disclosure, and The Lost World.
Were Michael Crichton's books popular?

Question: What was interesting about his books?
Self-contained rewrite: What was interesting about Michael Crichton's books?