I concur with many of the other reviewers who mention that this score is a departure from the others -- though still very much in the John Williams' genre of music. In fact, listening to some of the tracks ("Buckbeak's Flight" for example), I was reminded more of the soaring themes of "Star Wars" than of either of the two previous HP movies.
I own all three scores, and have no complaints against the first two, as a matter of fact. Lovely music. The score for "Prisoner of Azkaban," however, breaks new ground from the first two, and the result is a masterful and varied collection of music -- from the familiar "Lumos" to "Double Trouble" (featured in advance advertisements) to the haunting strains of "A Window to the Past" and so on, through the rest of the score, Williams has upped the ante to create a truly remarkable musical journey. This third volume makes me eager to see what kind of music Williams could create someday for the complex and emotionally-laden "Order of the Phoenix".