Interesting and valuable as a primary source of slave society and plantation life in the deep south before the Civil War and certainly a counterbalance to Frederick Douglass's own narrative. Northup's odyssey is the opposite of Douglass's - a horrifying descent into servitude that inverts the slave-to-freeman narrative that is more well known to modern audiences. The narrative catalyzes strong emotions in the reader, primarily toward the beginning. It's visceral, scary and infuriating. It's also pretty amazing how numb you can become as the story plods on from despair into acceptance. Like Northup, the reader learns not to become too hopeful when chances of escape appear and to tolerate and even find decent qualities in individuals that in ordinary circumstances we would loathe with every fiber of our being.
There is a flair of the grandiose in the telling of the story that belies some premeditation and takes away from some of the grittiness, "reality" and immediacy of the story - but hey, that's a literary criticism, not a denigration of the man's experiences or coping mechanisms by any means.