Let's be honest: that fourth star was given simply because of the setting: a living history museum. The first two chapters had me in hysterics. I know way too many people that are exactly like this, both teens and adults.
Chelsea is a great character: a little rebellious, not super thoughtful, and still trying to figure things out. In other words, a typical teen.
I'm not sure if folks who don't have a connection to living history will love this quite as much, but I've already started recommending it to all sorts of friends.