David McCullough, John Adams. Could have been a bit shorter, and I admit that I used it to fall asleep a few times. But I loved Adams - his moderation of thought and his independence - and I even enjoyed his inconsistencies, his vanity, and his moodiness. I liked that he was self-aware enough to admit his faults to his wife. I really did fall in love with Abigail Adams. If I was going to do it over, I'd probably read the Wikipedia article on John and get a collection of Abigail's letters. So many letters, to so many people, crossing oceans; really remarkable. Without the letters, the book would have been a dry recounting of official record; with the letters it sometimes had the gossipy feel of a novel or movie. The most suspenseful subplot was the relationship between Adams and Jefferson (and it had a happy ending, too, which was nice).
One fascinating thing was how much illness was a part of the story: so many children dying, adults suddenly taking ill, the widespread fear of epidemics, and seasonal illnesses that we have no conception of today. Infectious diseases lurked in the corners of this book - typhoid, diphtheria, tuberculosis, pneumonia, malaria - sinister characters picking off the players like snipers. I'd forgotten that the yellow fever epidemic in Philadelphia happened when George Washington was president and displaced the entire Congress, and I had had no idea that Dr. Benjamin Rush was one of Adams' closest friends.