I used to work at Barnes and Noble, and I had to read the first chapter of Harry Potter and the Sorcerer's Stone (I'm in the US)... my first thought: "GOSH this is dull!" Second thought: "This is so British!"
Fast forward a few years... It was my turn to pick what movie we would go see for date night, and there weren't just a lot of great choices, so we went to see Harry Potter. I liked it. Fast forward another year: I'm looking forward to the CoS movie. Watched it, and decided I needed to read the books. NOW I'm hooked.
J.K. Rowling has the most complex writing style of anyone of our time. Your brain has to really really work to comprehend half of what she puts in her books, and every time you read it, something new pops up (and I love rereading books anyway). She's got a great sense of humor, Harry and Ron are realistic teenage boys, and the other characters are so likeable (or hateable)!
It's not just Harry, Ron and Hermione that I like. Dumbledore, Lupin, and McGonagall are
awesome good guys, and Snape and Lucius are so dispicable! And, just like in real life, everyone has good and bad in them... I can't stand reading books or seeing movies where the heros have no flaws, and the enemies aren't likeable in the most remote sense.