There is definitely an art to writing interesting marginalia however. Perhaps something that requires practice?
Sam Anderson's would be intriguing I'm sure. Dick Macksey's marvelous. Anderson provides the example of people wanting books from [[Samuel Taylor Coleridge]] earlier in the piece.
I can only contrast this with some of the crazy minutiae an pedantry I've seen on Hypothes.is which makes me think that it's surely an art form.
I suspect some of it is that I'm missing the personal context with a particular person---a sense of continuity. Things get even worse when it's a piece annotated by a class which can create a cacophony of annotations. I see far too many "me too" annotations floating around in the margins that don't add anything to the conversation. (Hopefully I'm not guilty of this sin myself, but really, even my public annotations are a conversation between me and a piece and are only for my own benefit.)