"Occupied in observing Mr. Bingley's attentions to her sister, Elizabeth was far from suspecting that she was herself
becoming an object of some interest in the eyes of his friend. Mr. Darcy had at first scarcely allowed her to be pretty; he had looked at her
without admiration at the ball; and when they next met, he looked at her
only to criticise. But no sooner had he made it clear to himself and his friends that she had hardly a good feature in her face, than he began to find it was
rendered uncommonly intelligent by the beautiful expression of her dark eyes. To this discovery succeeded some others equally mortifying. Though he had detected with a critical eye more than one failure of perfect symmetry in her form, he was forced to acknowledge
her figure to be light and pleasing; and in spite of his asserting that her manners were not those of the fashionable world, he was caught by their
easy playfulness. Of this she was perfectly unaware; -- to her he was only the man who made himself agreeable no where, and who had not thought her handsome enough to dance with."
You are right:
"S" is sensing and "N" is Intuition.
They stand for the way a person takes in information,
whether in bits and pieces of fact [S],
or whether globally in one big picture [N].
We can't really isolate one dimension of the personality for our purposes here because the other dimensions interact with each other
An ISTJ is a Phlegmatic personality which is much more social by nature than an INTJ which is more Choleric by nature, and almost anti-social.
And I didn't think ISTJ were given to haughtiness, which INTJs are.
Except for those two things, Darcy seems more ISTJ.
Besides, INTJs are naturally very selfish, and I don't think Darcy is, or else his housekeeper would not have been able to say all those nice things about him.
He could be either; perhaps he is a mix.
Here are some descriptions of the types:
http://similarminds.com/software.html