After having the good luck to see Norton Juster recently, I picked up a copy of the annotated version of one of my childhood favorites. It still is one of the best books I've ever read (of any genre).
It isn't only that Juster did his homework on the framework for this story - as evidenced by many of the annotations by Leonard Marcus - it's that he could put himself in the head of a child so well. That he could remember his own struggles and triumphs as a child. And that he could roll those experiences into a book designed quite clearly to gently teach a child the benefit of learning. It probably helps that he was avoiding writing some other book (which he'd been funded for) to write this one!
So, word plays and math puns aside, it's astounding to me that he was able to write something now considered one of the dozen or so best children's classics of all time, without having written anything for children before that. That's talent. As is Feiffer's - those illustrations are so perfectly perfect (and the annotations do an excellent job describing Feiffer's genius as well as his deficiencies, and how those deficiencies ended up being genius for this book).
The annotations themselves are sometimes, oh, a bit too erudite or off the mark. In most cases, however, they were illuminating (I particularly like the explanation of why you clink glasses with people when making a toast). Not as good as the Annotated Alice (what could be?), but fine enough.