The Harry Potter series by J.K. Rowling
As I said, I have celiac disease and am always in a lot of pain. With reading, I was able to escape that. I read the series in second grade. I've always been an avid reader, so I was used to the looks that people gave me. The Harry Potter series has great character development, great world-building. Hah! No, it has AMAZING character development and AWESOME world-building. In case J.K. is reading this: I'M STILL WAITING FOR MY LETTER!!!! This is a great series and I recommend it to everyone everywhere. My personal favorite is the last one, but that's only by a little. I'm pretty sure the fifth is my next, though both answers probably will change.