No, it is not an unbiased report of the war by an objective outsider. It is a personal memoir of a man very deeply committed to the rebel cause.
As I have said several times here, my favorite Civil war book is his memoir, as edited by Professor Gallagher: Gallagher, Editor, Fighting for the Confederacy: The Personal Recollections of General Edward Porter Alexander.(Chapel Hill, NC: The University of North Carolina Press, 1989.)
Is it reasonable to expect any of the men who fought in this terrible conflict to be unbiased in relating their experiences years later? For that matter, will we be able to give an unbiased account of what we are currently doing years from now?
No, it is not objective, but it is an interesting work that gives us insight into how one man saw his war experiences. That is its lasting value.