What makes a book 'good' and why?

Of course a book with a topic your interested in reading about. Its like a movie it has to have a good story line. It has to flow well. Keep me interested in the end. For me personally I can get bored with a book easily. Usually I read Romance Novels, Inspirational, Biography's, and some others. I guess I have to walk away from the book with more knowledge when I opened it unless its a romance novel. Oh and a book most certainly trigger your imagination.