This book is fun. I enjoyed it a lot, and I know that I would have gone nuts over it if I had read it as a ten-year-old instead of as an adult. The author has a wonderful sense of humor. There were several literal laugh-out-loud moments. Percy is a very likable character, and I think a lot of kids can relate to his struggles with school and his conflicts with his obnoxious stepfather.
My favorite element of the story was the fact that the characters' "disabilities" were actually strengths or coverups for something awesome. The wheelchair was actually hiding the fact that the man in the wheelchair was a centaur, ADHD helps kids become great warriors, that type of thing. I thought it was clever, and it sends a good message to young readers.
This book is very similar to Harry Potter, so if you liked those books, you might like this one. For adult readers, a lot of the plot twists are predictable. I was always a few steps ahead of the characters. They kept making the same stupid mistakes over and over (and over). Young readers probably won't notice this as much as adult readers.
If I had to pick something that I didn't like about the book, it would be the editing and printing. There were very obvious typos and errors. The words on some of the pages were blurred or smeared. The ink had bled through the paper in some places. It made me very happy that I'm not dyslexic. C'mon, Disney, if you want to publish books, you'll have to do better.