Lots of creative fun
The heroes of these books, George and Harold, are hardly good kids, endlessly pulling pranks and annoying people. But when there is a problem, they do whatever it takes to set things right, whether or not they are at fault. They are very creative, they don't take things personally, and they are quite forgiving and good-hearted.
George and Harold do love potty humor, which I know annoys a lot of parents. My daughter thinks it's hilarious, and who am I to tell her what is funny? We talked about what is appropriate to say around people, and what might make others uncomfortable. And while potty humor isn't my thing, there is enough humor for adults that I don't mind when she reads them to me, which she insists on doing fairly often.
I get the feeling Dav Pilkey genuinely likes and understands children, and the "About the Author" section makes it sound like the books came from his own childhood imagination. With so many moralistic, sanitized children's books for sale, I thought it was a relief to find some that were purely for fun.
I know a lot of parents give these books to reluctant readers, but enthusiastic readers also like them. They also invite kids to make up their own superheroes and villains, and to try drawing and writing stories.
The violence is cartoony, but it is in there, and parents trying to minimize exposure to violent stories might want to give them a miss.