I am the reader of the family and, while books are not uncommon, they aren't the blood of existence for my siblings, but they are for me. My brother's question made me wonder what it is about books that makes them so enjoyable, not only the first time but for the second or fifth time as well.
Here, I think, I are three key things in every great book:
1. There are some books where the language is beautiful and arranged so cleverly that you have to giggle every time you see the subtle play on words or the careful arrangement of adjectives. These are books that somehow use language to generate an entire aura, a mood that you live in while reading the book. These are the masters of their genre.
Samples from Harry Potter: The names, of authors, characters, books, and etc. as well as the spells and enchantments, the play of the name Voldemort. Look particularly at the beginning of books 1, 4, and 6 where the first chapter is removed from the rest of the book, with different characters and places, but how that one chapter functions almost like a solo-story where the language is particularly spot-on and the connections between people, objects, and adjectives function beautifully. Also, you will find, that descriptions grow with the series. The first book actually does not use that much description, but just enough to give the idea then let the reader take the wheel and picture it for him/herself. Then with each progressing year the details are slowly added so by the end of the series the images in your head are distinct and clear.
2. There are other books that resonate because of the story. The action, the conflict, the climax, the resolution. These are the books of adventure, of plot twists, of the pacing heart. They nab you and yank you down an exciting road that leaves you exhilarated and out of breath.
In Harry Potter, I think the excellence of the story is obvious. One thing I love are the things that span the connection of the years, like how Nearly Headless Nick smashes the vanishing cabinet in book 2 that Malfoy tries to fix in book 6. Then Mafalda Hopkirk, who is the woman who sends Harry his underage wizardry warning in book 2, is the same woman Hermione impersonates in book 7 when they sneak into the M.o.M. So much enjoyment.
3. There are books you love because of the characters. Though written by one human, somehow these characters expand out of the binding and become real and dimensional. They question, they hurt, they struggle and you love them fully because, somehow, miraculously through words alone, you know them.
The characters in Harry Potter are absolutely fabulous. The main trio all go through the growth of young kids becoming solid adults, but there's also the side characters that develop as well. Malfoy is my personal favorite, how he grows up trying to be the good his parents believed in, but then how hard it is and how he can't go back and they're all stuck but he doesn't want to do it anymore. He does what he can and is still kind of a jerk, but that just makes him more believable. Ginny is always great, how she's a small character, and shy, then becomes this total babe that all the guys are after. Molly Weasley, oh you just feel for her sometimes. And Snape. We can never forget him.
The best of books combine these three traits and use them to their fullest extent. Harry Potter is a work of magic, with clever word play and juxtaposition in a story that is intricate, layered, and involved, with characters that grow, change, and are honed into amazing people you can't leave behind. So yes, I am obsessed, but only because I have fabulous taste.
