I re-read Prep by Curtis Sittenfeld this week while on vacation. I just picked it up briefly, and then fell into it (just like I had the first time) and decided I need to read the entire thing again. It really is a fantastic book. It's impossible to put down.
Lee, the prep school protagonist, is definitely a well-rounded, realistic character. Sometimes she was so frustrating I wanted to reach into the book, grab her by the shoulders, and shake her. She's so passive, such an observer, and so frequently judgmental (and often wrong). But her thoughts about how high school boys relate and flirt, how people of different classes interact, how adolescent girls often feel, are spot-on. And the other characters in the book seem so real, as well! Everyone in the book is a complete, full person. I buy all of it; nothing pulled me out of the story and said "this is a book, a work of fiction." That's why it's so hard to put down. It's less like reading a story and more like immediately falling into someone else's head, into their life. I recommend it so much.