I'm sure 80% of the girls from Austen's generation to mine were in love with Mr. Darcy or Mr. Knightley at some point of their adolescence. I was too. Darcy was my first biggest crush. We used to fight over him, and discuss him with aaahs and ooohs. I've read Pride and Prejudice more than 50 times, and I can almost quote all of his dialogues. With that expertise, I can tell with certainty, that Darcy wasn't that well described, apart from his "tall, handsome man of a large fortune", "proud and abominable" and the various 'meaningful glances' and observations he made, there was not much else about him.
Yet, I still sigh over him. And we (the 80% of us) still hope for someone like him.

Why? I think, what Darcy had to offer was stability. He held on. Even after the worst rejection, he hoped, and loved. He loved her for her imperfections - which he saw as perfections. And he found her quirks adorable, though he might sigh over them. He knew his worth, and he also knew when to say sorry. And he was ready to go that extra mile for the woman he loved.

That's it, that's all we all want.