Harry Potter's adventures take a darker turn in this 4th book of the series. The imagery and magical violence conjured in the text may be too strong for young readers. The teenage angst common in young adult books is very present in this volume. Harry finds friends who turn out to be enemies and enemies who turn out to be friends. He seems unable to decide who to trust. To make things worse, Ron gets angry with Harry (over Harry's fame and fortune) and ignores him for weeks.
Hermione takes on a crusade against prejudices of all kinds in this volume. Fans of the movie may appreciate this deeper look into Hermione's psyche. Another difference between book and movie is in how distant the teachers seem in the book. Snape is even worse to Harry in the book than ever in the movies, Dumbledore and McGonagal seem to hardly notice Harry's troubles and rarely help him. The only teacher seeming to help this year (besides Hagrid of course) turns out to be arranging Harry's death. (What's a year in Hogwarts without someone trying to kill Harry?)
This book, like all the others in the series, is well worth the read.