I have to agree with the other reviewers. Hank was an interesting character and the story did a good job of showing his difficulties with social interactions and fixation on music. On the other hand, Liana just didn't ring true as a character and that dragged down my overall rating of the book.
She's a girl who is intelligent enough to be working on a college level study during the summer. She admits to have kissed a number of boys and liking it, but it isn't clear how much further any of these relationships progressed. I think at one point she mentioned kissing a guy when they were both shirtless, so she may have on occasion done some moderate "hooking up" but she is still a virgin. From what she says it is kissing guys that she enjoys, not anything else that might progress from kissing. She rattles off the names and locations of a number of guys she's kissed over the years but there is never any indication that she has developed any sort of "reputation" around school for anything she has done. Then she gets an anonymous note accusing her of being a slut and suddenly she gets plagued with doubt and self-recrimination. The thought has never occured to her before and now all of a sudden it turns her into an emotional cripple.
Sorry, I just couldn't buy that this highly intelligent girl is going to suddenly equate liking to kiss guys with being a slut. Especially just based on an single anonymous word stuck in her locker when there is never any proof it was even intended for her. That she then fixates on enough to carry the note around in her wallet so her mother can conveniently notice it and add to the drama. And because she is a budding scientist, she decides that, rather than rationally examining the note for how meaningless it really is, she is guilty of unacceptable behavior (in some unknown person's eyes) and must therefore redeem herself in the guise of calling it an experiment.
Overall, consider it a 4 for Hank and a 2 for Liana.