A few people have said it, but Harry Potter is a classic series. Rowling's investment in building the characters and the universe is astounding. I finished the series a few years back after having read the first four books as a kid and just being satisfied with the remaining movies to fill the gaps. When I finished grad school and realized I could read whatever I wanted, I went back to the last three books and was not disappointed. They were just as epic as an adult that I believed they were when I was a child. There's a whole Wizarding World to invest yourself into too. Between the unique vocabulary and the awesome character development through the years, in my opinion, this fits what you're looking for.