At the end of this book, I was reminded of the end of _Burn After Reading_.
"What have we learned Palmer?"
"I don't know sir"
"I don't fucking know either"
"I guess we learned not to do it again"
I'm not sure if it was the fault of the book or of the war, but it really seemed like a giant muddle all the way through with no really clear lessons. Even examining someone like McClellan, who manages to exceed Joffrey Baratheon in sheer douchiness, and it is not clear what the correct course of action at the time should have been. For all of his horrible faults, McClellan did keep the Union line together and prevent a decisive Southern victory long enough for the northern war machine to get rolling. It's possible that with a more competent general, the dice would have fallen differently and prevented even that. So, a ton of mistakes, many poor/traitorous generals, toxic command relationships, key military decisions botched due to election politics, plenty of friendly fire, and communications tech that could not keep up with the tempo and scale of battle. Lincoln and Farragut are about the only ones who come out of it looking like adults.
Overall the book seemed perfectly acceptable. My main criticism would be that it needed more/better maps (i.e. show the positions as they develop rather than a single image of a single point in time), and maybe some diagrams of the command hierarchies at various points. This would be much clearer/faster than trying to convey the same information in type.