As a novel by Jane Austen, "Northanger abbey" is quite weak. But, if it's difficult to put into words where her greatness is, as Virginia Woolf has said, "of all great writers she is the most difficult to catch in the act of greatness" for it's in the nuances, the smallest details, it's equally difficult to say exactly why I find "Northanger abbey" inferior to her other works, particularly "Mansfield park", and guess that it's 1 of her weakest works. Many parts aren't polished or developed, and the book has a very hurried ending (like the ending of "Sense and sensibility").
Still, it is enjoyable and has many strengths, such as the parody of Gothic fiction, and the characterisation of Catherine Morland and Isabella Thorpe (the latter, in my opinion, is 1 of the best and most memorable characters in literature).
Update at 9.55pm:
In this article Joan Aiken discusses how Jane Austen might have revised "Northanger abbey". She also confirms my feeling that this novel is very much like an early work, because in spite of its own merits and the faults of "Sense and sensibility", and because of little revision, it's weaker in terms of plot, technique, characterisation... Compared to other works by Jane Austen, it's thinner and weaker and not yet to have a masterful control of the smallest details.
But, as written here, a more important difference is the attitude to life.
After listing, exploring the weaknesses of this novel and suggesting what Jane Austen might have done, Joan Aiken, however, concludes:
"Having conceived such a dislike of Bath as she did in later life, Jane Austen, I am sure, would, in a revision, have reduced the proportion of the story laid there. The move to Northanger would probably have happened much earlier.
What else? The bad characters would have become more unpleasant; the social stresses and tensions would have increased.
My expert audience will, long ago, have realized that I have laid down for Jane Austen a series of wholly conflicting and incompatible aims. If she had expanded her cast and introduced several sub-plots, it would be almost impossible to maintain the Gothic pastiche element, for an essential aspect of Gothic melodrama is that the heroine must be all alone and unfriended in the midst of mysterious perils.
If the society around her were blacker and more corrupt, the heroine, unless she were an absolute simpleton, must be aware of this. And she is no simpleton.
If there were to be a confrontation between Catherine and the General, then the ending of the book would lose its surprise. Also, once she had verbally set herself up against him, the conflict between them would be almost impossible to resolve, except by his death of apoplexy, and such a death seems wildly outside the author’s usual range; it is true that she has Mrs. Churchill die, and so resolve the problems of Frank and Jane Fairfax, but as she has never appeared onstage the reader’s sensibilities are not jolted.
If all the other characters were allowed to impinge on the hero and heroine, then we would lose the freshness and spontaneity of the relation between Catherine and Henry.
How would the author have solved such intractable problems? Who was Jane Austen writing for, anyway? In the early days, as I said, I am sure that she was writing for the entertainment of her family circle. Later on – though of course she continued to show her manuscripts to Cassandra and brother Henry, and in due course to the rest of the relations, I think that, basically, she was writing for herself, for her own critical ear. As a worker in the same medium, I feel that, very strongly. The revision that she made at the end of Persuasion, cancelling one chapter and writing in two more, shows us how acute and precise, even during severe ill-health, that ear remained. She could not tolerate sloppy workmanship.
I think she realized the irreconcilable problems that a revision of Northanger Abbey would present; she could see, all too clearly, that if she began reshaping its framework, the story would lose its fun and engagingness and early sparkle.
What it would have gained, who can say? But we can only salute the integrity that decided her to leave it alone, not to try and improve on it. (Or maybe, of course, like many writers, she had grown impatient with editorial messing-about, and wanted to get on with the next work, with Sanditon.)
Whatever the reason, she has left us an exuberant, faulty masterpiece, and that is a great deal better than no masterpiece at all."
I wouldn't use the word "masterpiece"- such a word should be used sparingly (Joan Aiken, after all, seems to be obsessed with her and wrote 6 Austen-inspired books). But this is an interesting point nevertheless.