I started reading them when the 1st movie came out. Because I knew I had to read the books first. I was hooked. I got friends hooked.
I was drawn to a lot of the themes & how they're viewed through this somewhat sheltered kid's eyes. Also, I love the wizarding world that JKR has created-fascinating. The characters do seem to be easy to love (or hate, in cases such as Prof. Umbridge
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I'm a really avid reader. I generally don't like girly books (a la Oprah' Book Club) so it's hard for me to find really good stuff. In fact, after awhile of HP, I found that I had a hard time going on to other books 'cause they weren't as interesting!
Also, for a long time the 3rd book was my least favorite. It wasn't until about the 4th or 5th read through that I really got into it like I did the others. Book 4 has been my favorite since I first read it. Although I've only read book 5 once, so I may change my mind.