Well, as much as I LOOOOOVE me some harry potter, I have to agree with ZeroMachine on the fact that the universe of Harry Potter isn't the most compelling. However, I have to give credit to Rowling for making what is essentially a highly advanced secondary school look awesome. I'll say that again: SHE MADE SCHOOL LOOK AWESOME. Regardless of the curriculum, that's a pretty awesome job on her part.
The whole mythos and universe of harry potter is essentially borrowed from other great fantasy works. Rifftrax made a joke about that in their riff of Prisoner of Azkaban: "For homework, find a copy of the Dungeons and Dragons Bestiary, pick a creature, slightly change the lettering and invent your own monster!" What I love about Harry Potter the most is that fantasy is not necessarily the book's biggest focus. To me, it plays out like every great children's detective story mixed with mid 90's teen sitcoms mixed with a dash of Tolkien and Martin.
The hook for me was Rowling's writing. She REALLY gave a lot of life to it. Her characterization and the slow molding of the stories and plot threads over 7 books is pretty damn incredible. While the ending of the whole thing was kind of a curveball-of-the-fates delivered by the righteous hand of God himself to your face, upon a second (and it wouldn't help with a third) re-reading, I was able to grasp and understand the complexities of it all; now looking back, what she created is nothing short of mesmerizing.
If you're looking for depth and a "mythos", going to the movies is definitely not where you want to start. While the movies I enjoyed, they can't hope to go as deep as the books did. Personally, I think a TV series would have been better. 7 books, 7 TV seasons. This would allow the writers to go nuts bringing about the insane depth and characterization of the books to life, and not being hampered by a silly 150 minute time limit.