By carefully re-examining the known documentary record and uncovering more than a few entirely new sources during the course of his research, Carretta has written the most complete biography of Wheatley to date, one I think is unlikely to be surpassed (barring the emergence of some significant new evidence in the future, anyway). He successfully "busts" many of the myths that have sprung up around Wheatley, and ably locates her within the dual contexts of the overall transatlantic literary culture of the 1770s and the nascent trend of publications by people of African descent in the Anglo-American world.
Carretta's explication of Wheatley's connections in and around Boston during the 1760s and early 1770s makes for fascinating reading, as does his chapter on her trip to London in 1773. He carefully mines her correspondence and writings for details of who she met, the sights she saw, the books she purchased, and how the trip affected not only the publication of her Poems but also her own legal status.
While much of Wheatley's post-manumission life remains nebulous given the lack of available documents, Carretta has done a great service by recreating those years to the extent possible. His research has revealed a great deal more about Phillis' husband John Peters than was previously known, and his discussion of Wheatley's married life (and what that meant for her public career) is most enlightening.
The useful notes and full bibliography (which together cover more than fifty pages) are vital parts of the book, and I'm glad (though not surprised, in this case) to see such complete documentation of the research process.