I don't know.
The historical detail (even acknowledging that most of it is speculation formed from historical records) is pretty amazing, and the subject matter itself is fascinating, but . . . this book just didn't do it for me, mostly because it felt like a giant collage of unrelated items instead of a coherent book on a single subject. The serial killer H.H. Holmes? Fascinating. The history of the Chicago World's Fair? Very interesting. The life of Daniel Burnham, who is apparently one of the founding fathers of Chicago? Pretty cool. Learning about the invention of the Ferris Wheel? Awesome. Together? Not so much.
The main problem is that the book's title, The Devil in the White City, lends itself to certain expectations, namely that Holmes and the fair are connected . . . and they're really not. I wish Larson would have written two books instead of one.