Anthonypeers, you probably read the books before you watched the movies. Everyone I've talked to who watched the movies and didn't read the books hates or simply got bored during the first two while the third movie (which, IMO, was the best of them all) on were well received by those who never read the books.
Books and movies aren't directly adaptable. They are entirely different mediums and even a 50,000 word novel filmed to be 100% true to the book would be at least two and a half hours long (far longer than the average movie goer wants to sit through). In order to make good movies out of the Harry Potter franchise they had to heavily rewrite the plots to make it conform to the different medium.
In the end you have to chose rather you want to make a movie completely true to the book, or make the best movie you possibly can. Harry Potter and the Sorcerer's Stone was very true to the book and not a very well received movie by those who didn't read the books, while The Jungle Book was absolutely nothing like the novel but was a great success by those who've never read it.