Northanger Abbey was Jane Austen's first book ever written and last ever published. I believe is was published posthumously and I'm not sure she ever intended for it to be read by an audience (although I have not read anything one way or the other). The book seemed to me to be a study in writing novels. She asked and answered a lot of questions in this book. What makes a heroine or a plot worthy of reading? Which works to take inspiration from, which to completely diverge from? Are novels worthy endeavors? Can one be written about normal people? Will doing so make novels more socially acceptable? Do popular opinions matter on the subject of novels anyway? Jane makes many asides to the audience which I felt were more of a stream of consciousness creative writing exercise than anything else. I especially felt that the book was not intended to be published at the end when she essentially said, "and then they all lived happily ever after, etc., etc. You know all the rest and I can fill it all in later without giving it much thought." It is possible that this was an underdeveloped stylistic choice, especially considering the similar though less abrupt ending of Emma. I think however, that Northanger Abbey was just a practice to help the author decide more precisely on a direction to take her work.
I didn't particularly like this book and I found the asides to the audience on par with political lobbyist soapboxes, of which I am not a fan. I am quite glad I had read a number of other Jane Austens before reading this one. I fear that I would not have picked up any of the much more worthy ones, had I read this one first. I don't think anyone should miss out on Austen but in this case I am going to have to say skip this one, at least until you have read some of her other more wonderful books.