This is just one of the ways that Chernow’s gift for condensation, unmistakable in earlier books like “The Death of the Banker” and even the hefty “Washington,” fails him after the first third of this 1,100-page book. By comparison, Justin Kaplan’s penetrating 1966 biography, “Mr. Clemens and Mark Twain,” which won both the Pulitzer Prize and the National Book Award, came in at a brisk 424 pages. Ron Powers’s more recent biography, “Mark Twain: A Life” (2005), a book that has more ragtime in its soul than Chernow’s, wrapped up the life in 722 pages. At the rate we are heading, Twain’s next overkill biographer will deliver a page for every day he was on the planet.

-Dwight Garner in the NY Times