It's powerful stuff - Jacobs describes the violence inflicted on slaves in detail, and gives a broad enough account of their sexual exploitation by the white population to appall the northern women who were her primary target. The key point, that she comes back to over and over again, is that slavery acted to destroy families; and unlike Harriet Beecher Stowe, who was constrained to give closure to Uncle Tom's Cabin by the constraints of the novel format, she can tell it like it is and also has the luxury of a narrative that stretches over decades, so it is all the more effective.
Despite her being deprived of formal education, Jacobs' style is fluent and eloquent; and any suspicion that there was a ghost-writer involved is laid to rest by reading her other writings available on-line - for instance her reply to a frankly awful piece by former First Lady Julia Tyler; here several of her letters to Harriet Beecher Stowe and others. Of the various slave narratives I have read over the last few years, I think this is the best.