Book: Harry Potter and the prizoner of azkaban

I chose this book because I like Harry Potter. I've ever seen Harry Potter's movies but I've never read these books. I like Harry Potter because it's not only a story of witches but we also see love and friendships between the characters. This story of Harry Potter's different from the others because there're a lot of new characters, like Sirius Black, the teacher Lupin..
I also like newthings like the magicbus, there back at the end of the book, different places where the characters are because those places are places that we've never seen before.
But there're several things that I didn't like. For example, the new Hagrid's house and his pet who is big and uggly.
I think this story's interesting but very long, too long. And for the children, I think it can make them scared, even if Voldemort, who's the meanest character, isn't very present in this story. I'd already seen the film Harry Potter and the prizoner of azkaban ,so I wasn't suprised by the story, but I appreciated it though. It's a little bit different from the film and I think I prefered reading the book.