Agreed! Just because a book is written in the style of a grandfather telling a story doesn't mean only "for children". I think that's a foolish thing to assert. (In fact, Tolkien literally said the book was not specifically written for children.)

To me, it was the most accessible book he wrote about Middle Earth, and it's the one I've reread the most. Even though it's still a bit rambling, it's a more succinct story than the others: fewer pages describing the prairies and grasslands etc.