Harry Potter gives off that lovely old fashioned - english feeling. Well the books do anyway. Like, the magic, old english, boarding school thing is really nice and magical, for want of a better word. And when you get really engrosed into that plot and the thoughts of the characters you really start to put clues together.
J.K. Rowling is a very good author. She can weave together a marvelously tricky plot and I think you really need to read all the books a couple of times to really get the plot and clues.
Apart from what I've mentioned, it's good because of the characters, settings, ideas...marvelous ideas, friendship morals, drama, theme. It's just a great series. What spoils it is people saying it's for children. I didn't realise for a while that yes it's theme is childish but the writing is bold and I certainly wouldn't be ashamed if I were 40, or whatever, and reading it, anywhere.
The movies have spoilt it to an extent. They've had to cut and simplify the stories so that it seems unnatural and the exciting, authentic and originality is gone. The movies make it seem so it's all about the stereotypical witches and brooms and cauldrons. But they also make clear the characters and settings and visually it's great to see these books you've loved for years up on screen with marevlous graphics.
The books are alway better because of the great detail that gets rid of one's sterotype of witches and wizards.