Shakespeare adaptations

If we stick to adaptations pre-1800, these books look like they'll provide plenty of background information:

Branam, George. Eighteenth-Century Adaptations of Shakespearean Tragedy.
In addition to a very practical complete index listing all the adaptations, Branam gives a good overview of general changes made by adaptations (such as elevating diction or reducing imagery). He divides 18th-century adaptations into three chronological groups.

Dobson, Michael. The Making of the National Poet: Shakespeare, Adaptation, and Authorship 1660-1769.
Dobson makes several broad arguments about thematic alterations in the Restoration revisions, focusing on de-emphasizing monarchy and emphasizing domesticity and family, among others. This has a lot of useful treatments of specific revisions, including The Enchanted Isle.

Marsden, Jean. The Re-imagined Text: Shakespeare, Adaptation, and Eighteenth-Century Literary Theory.
Marsden is not in our library, but most of this very useful book is excerpted on Google Books. It deals with simplifications and thematic changes in the adaptations, with an emphasis on how Shakespearean criticism drove the changes.

Fischlin, Daniel. Adaptations of Shakespeare.
This is actually an anthology, but it provides concise and helpful overviews before each of the twelve adaptations printed.