I read a large number of Dahl books with my kids. They are blunt, rude (by modern standards), filled with danger (consequences), comedic, and adult in a way that most children's books no longer are.

"YA" as a genre has been entirely taken over by women authors writing for women. Dahl gives kids something they rarely get to experience any more.

I also like the "Magic Treehouse" books, "Who Was" non-fiction books, Boxcar Children, Hardy Boys, Redwall (talking mice who protect an abbey from invading rats!), the Hobbit, Narnia, etc.

Piers Anthony "Xanth" is unreadable to me as an adult now, but there seems to be a certain age (middle school / high school boys?) for whom the slight sexual edginess, puns, and randomness is very appealing.