My daughter devours these books in one sitting. They're fairly fast reading. And my husband picked one up and was hooked on them as well (he's easily entertained, obviously). I recommended these to several people for their children, and all have loved them. All is not lollipops & sunshine in these books -- there are some scary moments, and parents in danger, so it's not for young children unless they are quite sophisticated readers. Our daughter is 9, and I consider them just right for her.
Graphic novels are always good for reluctant readers, drawing many of them in who might otherwise be uninterested, and these are top-notch books by a fabulous author/illustrator. We've gone on to buy the entire series, as well as his Explorer books.
A well told story with lavish full colour art work on each page. The books flow nicely to from one to the next. If only they were a little bigger! A must own for any graphic novel fans. I expect I will never resell mine and will keep it on my book self for future use. Hope this helps.