Once again, I must admit to being horribly biased. This book (and the three which come after it), was written by my dad.
The goal of the four-volume series is to present the final year of the Civil War in a strictly chronological format. Most history books, basic or learned, will follow events at one place for some time, before breaking off, going back in time, and picking up at a different location. This can muddle understanding of how events truly interacted with each other, as even with the time of travel being long, the telegraph often made communications fast.
This series picks up with Grant taking command of all the armies of the Union. His plan of campaign was for several coordinated offensives in the various theaters of operation. Thus, the series picks up the chronological viewpoint at the point where there is an actual attempt to conduct the war at several points at the same time.
The series is a re-ordering of data, not an attempt to bring to light new data, or new theories. It is written (quite successfully) in a readable style, and while it is good to have some familiarity with the outlines of the subject, it is not written at the level the serious scholar, but rather the interested hobbyist.