Prepare for a long VM.
Misty is a headstrong girl who starts out as a rather caring and helpful girl, but with a vicious temper and a stubborn attitude. She's a very relatable character, from her love of cute Pokemon, to her strong dislike of certain things(peppers, carrots, and bugs), right down to her silly fashion and romance craze, something all girls experience around that age, be it a girly girl or a slight tomboy. She knows how to stand up for herself and doesn't need to rely on a man's help, having grown up with three older sisters. As she develops, she begins to accept her relationship with her sisters for the way it is, knowing that even though she'll be the one to help them out, her sisters are willing to take care of her when she needs it, as they do care for her. This is a pretty good character development, as some would hold grudges against older sisters that they thought cared only about themselves, but Misty knows better than that. Misty, although she doesn't always show it, has a kind and gentle heart. She worries frantically about those she cares for, as shown for the times she was willing to risk her life for her friends, especially Ash. With Ash, she constantly clashes with him, yet inspires him to do his best. I believe she did an amazing job at keeping his confidence in check, raising it when he needs it most, and deflating his ego when he gets a big head. After a long time of traveling with him, and getting to know him, she started to harbor feelings toward him, forgetting her initial reason for traveling with him.(although I do find it a bit fishy that she only followed him around for her bike....most likely she was attracted to him even then) Along the way, she also be-friended Brock, and maintained his overly flirtaious attitude so that his true personality would show. Misty, while not the only influence, did a lot to keep her guy friends at bay so as to make them better people. In a way, Misty leaving did have one good side effect- they finally started to learn how to manage their behavior themselves, as Misty had for so long, often unappreciated at the time. Misty has shown impressive intelligence, as she was the one, not Brock, to figure out Blaine's riddles and spot right away when James was lying in his story. Also, she has that somewhat lovable side of jealousy that gives her the courage to defend her relationship with Ash, as shown throughout the series. She shares this desire with Ash to prove their worth to each other, sometimes shown through their constant debating, which while that can actually bring out the worst in their personalities, this can bring them to an important realization. An example of this is during the last episode of season 1. In this episode, Ash is already feeling ashamed of losing, and when Misty comes in and tries to cheer him up, he takes this as pity and lashes out. In order to defend herself, Misty continues to argue with him, and later Ash sees how mistaken he was for acting that way.(although I disappointingly saw no apology directed to Misty, but I suppose that's a pride thing)
Too much? I could probably write more, but you might get sick of my Misty/Pokeshipping-filled ranting. ; )