The books are really good YA books way before that genre got raped to death by publishers, topped off with a satisfying ending by an author at the top of her game at the end of something she clearly planned out (well.) (It's unfortunate how sharp the drop off after that is, though...)
The movies are serviceable-to-decent PG-13 action/YA flicks elevated slightly by a cast of pretty stellar veteran actors and increasing budgets. Prisoner of Azkaban, having been directed by Alfonso Cuarón (Children of Men, Gravity), is the best of the bunch and great just on its own merits.