It’s just ok.
The author is no military historian, so his description of battles was pitiful and would be confusing for anyone not already very familiar with the various campaigns. The author is also extremely biased toward Grant, ignoring or breezing over many of his failures and missteps and petty moments during the war and after. The worst part is the author’s hand waving of some events that don’t reflect well on Grant. He makes Cold harbor sound like a little oopsie that was over in a few hours.
The author also has a bad habit of diminishing other Federal officers to build Grant up. Often very unfairly. Not ok to do for a bio that’s supposed to focus on the man’s inner life and character. I’m not trying to shit on Grant. He was only human, after all. And he was certainly the yankee government’s best commander of the overall Army.
There is nothing new or insightful in it. Everything in it and more can be found in Grant’s autobiography.
My advice is to skip this one.