Books are just dead words on paper and it is the readers who bring the stories alive. Previously, writers wrote a book and sent it out into the world. A couple of months after publication letters from readers might arrive. And, leaving aside the professional reviews, it is really the reader's opinions that the writer needs. They vote for a book - and a writer - with their hard earned cash every time they go into a bookstore (or online - that's my age showing!) and buy a book.
I am of the generation of writers who can get instant feedback from readers within hours of publication. The fan forum is extraordinary - readers from all over the world coming together to discuss, argue and debate scenes and characters from a novel. They add a layer to the story that I cannot write and yes, I will participate in that conversation and answer questions. After all, they are the people I'm writing for and their enthusiasm and questions really pushes me to raise the bar.
Making sure that the geography and timelines work is always the hardest part of writing. But you owe it to the readers to get it right!
I have a huge music library and deliberately choose the piece of music to match the piece I'm writing. So, every book I write has its own "soundtrack."