I've had the Cambridge edition of Shakespeare's complete works sitting on my bookshelf for a while, and finally got around to sitting down and flicking through the copious and interesting notes contained in the text. These were written by the editor, John Dover Wilson, who put considerable effort into attempting to correct the errors in the printed scripts by various means; for example, he made a detailed study of Shakespeare's handwriting and the types of misreadings that a printer would make.
This book is Dover Wilson's examination of some of the odder points in the plot of Hamlet in the light of his analysis---most of which can be cleared up by reverse-engineering the stage directions omitted from the standard text. In the case of Hamlet, the multiple versions of the text provide considerable illumination: the "first quarto" version largely paraphrases the text, but in doing so often gives senses and emphases that are not obvious in the folio version; the early German adaptation "Der Bestrafte Brüdermord" similarly mangles the text, but preserves much of the contemporary staging approach.
This is an interesting and accessible read, and generally made the play make a lot more sense to me; thoroughly recommended.