A one-volume military history of the Civil War, encyclopedic in its detail.
This would probably work best if used as a reference work rather than a book to be read from start to finish -- an undertaking I think most readers will find impossible. The level of detail, including lists of armories and types of ammunition, is daunting.
I finished the book with a number of concerns.
Firstly, Eicher is not a professional historian but an astronomer, and while that certainly doesn't disqualify him from making a valid scholarly contribution, it does make me a little cautious about his credentials.
It's ironic that Eicher chooses to criticize the "dated" prose style of Bruce Catton. LONGEST NIGHT is written in a style that is so dry that I think even highly motivated readers will have trouble getting through the book. Some of Catton's theories may be dated today, but his prose continues to make the Civil War come alive, something that cannot be said for Eicher's.
I found various minor errors in the book, ranging from an oddly skewed version of the Battle of Port Republic to a mistaken source for Jeb Stuart's nickname, and I wonder if, since I found errors on topics I've studied, if there may be greater problems lurking in the background. As well, it's not always clear why Eicher chooses to discuss some events in exhaustive detail and not others -- returning to the cavalry as one example, why give all of John Hunt Morgan's raids in exhaustive detail, but accord almost no discussion to Stuart's rides around McClellan? Perhaps my most serious concern, though, is with Eicher's frequent attribution of emotional states to historical figures without any supporting evidence. For example, he describes Longstreet as "grumpy" at Gettysburg, Lee as "desperate", Mosby in 1864 as "in a sour mood". Especially given that Eicher tries to causally connect these moods with the military actions of the people in question, it worries me quite a bit that he cites no supporting dispatches, letters, diaries or memoirs.
Eicher offers somewhat limited analysis, sticking mostly with a recitation of facts; he does state that he feels it would have been impossible for the Confederacy to win the war, but doesn't, in my opinion, offer convincing arguments why not.
I recommend this only with reservations; there are better, and more enlivening, books in print.