Harry Potter and the Prisoner of Azkaban is probably my least favorite of the Harry Potter series (although it's still fantastic). To me it feels stuck between the more youthful style of the first two books and the steadily maturing theme in the later books. This is also the only book where Harry is not faced against Voldemort, which is a nice break from the "everything has been going wrong it turns out you need to fight Voldemort at the end of the book" formula that runs through the books. The Serious/Dementor plots are not my favorite and overall this is the book I've read the least.