She's bossy, excessively enthusiastic about pop quizzes, and the most irritatingly talented kid in the class. She's also brilliant, keeps her cool in a crisis, and will fall on a sword for her friends without a moment of hesitation.
On the surface, Hermione is precisely the prickly cactus fruit you don't want to mess with. She knows it all, and can't be bothered with social niceties—she simply says it how it is. Harry and Ron are both clearly irritated by her from the start.
Ron shares little jabs at her with his friends, and Harry quietly concedes a number of times before Hermione accidentally overhears Ron:
RON: Honestly, she's a nightmare! No wonder she hasn't got any friends.
Ironically, of course, it's this comment that secures the fact that Ron and Harry become her lifelong BFFs…although Ron's a teensy-weensy bit right about Hermione being a "nightmare." (Our nightmares are all about bossypants teacher's pets.)
This comment also advances the plot of this movie a whole lot. Hermione misses dinner and the boys learn that she has been crying in the girl's restroom all afternoon. And when You-Know-Who lets the troll out, Ron and Harry realize that Hermione isn't with the escaping students.
The battle in the bathroom with the troll is the real turning point for what will become one of the best trios of friends one could ever hope for. Hermione tells a complete lie to the teachers in order to keep her friends out of trouble for nearly getting themselves killed to help her.
So beneath the snooty exterior, Hermione Granger has a heart of gold: she's as brave as anyone and ready to put it all on the line for her friends. And as she grows over the course of the story, her cleverness grows as well. Look at the way she lies to McGonagall and the other teachers after the troll attack:
HERMIONE: I went looking for the troll. I'd read about them and thought I could handle it. But I was wrong. If Harry and Ron hadn't come and found me, I'd probably be dead.
This whopper demonstrates more than Hermione's willingness to bend the rules. It shows that her adherence that book learning solves all life's problems has its drawbacks…and that she needs to expand her horizons beyond the library if she's going to appreciate just how marvelous her friends are.
And this realization allows her her give Harry a big boost of confidence just before he goes in for the final confrontation with Voldemort:
HERMIONE: You'll be okay, Harry. You're a great wizard, you really are.
HARRY: Not as good as you.
HERMIONE: Me? Books and cleverness? There are more important things. Friendship, and bravery.
Hermione is at her most Hermione-eriffic at this point. She knows how good she is, but she also knows that her skills aren't always the most important. She's a boss, but that doesn't mean that other people can't also be bosses.
Hermione also shares the stranger-in-a-strange-land fascination that Harry Potter has towards the wizarding world. Her parents are both Muggles, but girl learns fast and has a clear advantage over Harry when it comes to good old-fashioned book smarts. We're not sure if Hermione had more time to read up before her trip to Hogwarts, or if her hunger for knowledge simply fueled an already voracious appetite for very heavy non-fiction books.
Her ability to accumulate knowledge and retain it proves useful to their endeavors time and again. From simple charms and spells to historical facts pertinent to their success, Hermione's always there and ready to use her many talents. We see this in the finale, where she gets the trio through the strangling vines thanks to her judicious use of her studies (and some fairly snazzy wand work).
And you just know that Hermione's A-student skills are going to aid the fight against Voldemort time and again.