The Perks of Being a Wallflower is about the freshman year of a boy named Charlie. Over the course of that year, he makes new friends, experiments with drugs, experiences literature and film, gains and loses a girlfriend, and most importantly, learns about himself. It's a deeply touching book. Since everyone has been a teenager, you can relate in some way to Charlie's story.
I'm also adding this article from A.V. Club about how Perks holds up with adult readers. I think it's well written, although with a little salty language, and does a much better job with the review than I could.
