I really enjoyed this when I first read it, and even on a couple of subsequent rereadings. It *is* an interesting story, told well, as most of RMB's stories are.
BUT...I just finished reading Octavia Butler's "Kindred", which, based on non-fictional sources I've read, is a MUCH more accurate contemporary depiction of what slavery was actually like (although it, too, is historical fiction). The slaves in "High Hearts" are certainly not thrilled to be slaves, but they love their white masters, and the white people (with a few exceptions) are all basically just misguided, benevolent matriarchs/patriarchs -- no whippings, no deprivation, and they really seem to believe that the slaves are better off under their care than they would be as free people.
Brown's afterword, too, reeks of Southern white apologist; as herself -- not even in the context of the story -- she insists that the Civil War was not about slavery, and that if it had been, there wouldn't have been so many poor white people fighting for the South...but even a cursory bit of actual research (using non-Southern sources) should be enough to dispel that notion.
So I give it two stars because, as I said, it was an engaging story, but for someone who was supposedly big into the civil rights movement in the '60s, Brown is incredibly tone-deaf about the South's role in the Civil War.