This in my opinion is Jane Austen's lightest, yet one of the most satirical novels. She is much better in later novels in terms of story composition - here, she sometimes picks up threads never to properly explore them. But its in-your-face satire never ceases to amaze you.
Northanger Abbey was Jane Austenís first finished novel, though it was published much later. As such, you can see the author's ideas in formation, which will get matured in later works. You can see the thoughts uppermost in her mind - her defence of female novelists, her contempt of marriages based on financial motives, her pshawing social mores, so much that she doesn't spare even the hero and heroine of the story.
A must read for Austen aficionados, optional for the rest.