One distinction is that the voice of Jane Austen the narrator is perhaps picked up more clearly here than in her other novels. Here you will find, for example, her minor dissertation in praise of the novel, "... work in which the greatest powers of the mind are displayed, in which the most thorough knowledge of the human nature, the happiest delineation of its varieties, the liveliest effusions of wit and humor are conveyed to the world in the best chosen language".
A second quality is the strong sense of location that emanates from its pages. Jane Austen is rarely a travel guide, but here she conducts the reader around the small English city of Bath.
A third excellence is its depiction of its "heroine" Catherine Moreland, a 17 year-old who gradually learns that reality is not the same as it's depicted in Mrs Radcliffe's novels.
And so it is great fun to read of the novel-reading heroine Catherine finding mortifications and infatuations in Bath. It is fun also to see if "something must and will happen to throw a hero in her way".
"Northanger Abbey" is a good first novel but it is by no means Jane Austen's best, and Catherine is not as interesting a heroine as Elizabeth Bennet, Emma Watson or Elinor Dashwood; she's a somewhat shallow, undeveloped young lady who lacks their depth and their intelligence. But she's a likeable heroine; unlike Fanny Price, Catherine doesn't try to be perfect nor judge others for failing to be so, and unlike Emma Watson, she's not meddling in everyone else's business. She can admit when she's at fault and she has a generous spirit. We like to imagine her as the tomboy Austen pictures her in her childhood, rolling down hills and chasing her brothers and sisters. Austen provided a number of interesting supporting characters: Henry's amiable sister Elinor, his insufferably snobbish and narrow-minded father General Tilney, and the artful, heartless flirt Isabella Thorpe. By the book's end, Catherine has grown up a bit; she sees life as it is and realizes Henry's steady common sense is infinitely preferable to the histrionics of any Gothic hero. Jane Austen's first book was a promising introduction of better things to come.