Little to add to the detailed praise in other comments, but having just finished the print version I would add that all that praise is well deserved. An incredible, detailed, and yet highly readable account of the man who, with Lincoln, saved the nation. Others have commented on how partisans for the "Lost Cause" myth have maligned him, and how Chernow restores his reputation.
One other comment: Chernow rightly comments that the era of Reconstruction has been forgotten and misrepresented for over a century. "Grant" rips away that veil to show the horrors perpetrated on black citizens by their Southern neighbors. Understanding that history is essential to understanding how it still influences us today.