Just finished it! Surprising is a good descriptor. I think I'll take a lot of useful lessons from it. I didn't expect to see my own "methods" staring back at me, so that was pleasing. Of particular note is his suggestion about writing for the love of it. I have no ambitions to be a famous author, I just enjoy writing because it's fun. Crafting a world, and the characters. Setting them loose and seeing what comes of it.
I enjoyed On Writing. It's the book authors tell you to read. Editors tell you to read Stein on Writing. My editor told me to read John Gardner's "On Writers and Writing". Stephen King's book will teach you how to make writing fun. Stein's book will teach you how to make writing a successful pursuit. Gardner's book will teach you why both matter. Of the three, I read King twice, Gardner once and Stein three times.