The book combined a few of my favourites in romances:- 
 1)History 
 2) The heroine loves to read. Do I hear seconds when I say that it is easier to imagine yourself being wooed this way, in the story? :P 
 3) The heroine has a life apart from just romancing in life. Not that romance isn't important. 
 4) There's a hunk of a Scot. I like Scots verra verra much :D