I have enjoyed a number of Winchester's books, but this was not one of them. He is at his best when he is detailing a story that is not well-known and surprising. That was what drove the success of his previous work. In this book, he takes on an enormous subject and ends up with a catalog of his research interspersed with totally unsupported assertions and some rather dull writing about his travels.
The structural problem with the book is that Winchester has chosen a cumbersome thematic structure to organize his writing: the seven stages of man listed in the "All the world's a stage..." speech from As You Like It. While this may have seemed like a clever way to tackle a sprawling subject like the Atlantic, the structure overwhelms any insight Winchester may or may not have had about the Atlantic. Seeking to fill this outline, Winchester stuffs everything into it that either (a) features the words "sea" or "Atlantic" or (b) happens to have taken place in or near the Atlantic. The result is a combination of the obvious (jet travel ended regular ocean liner service) or the downright tautological (in a section on "cities," Winchester writes brief descriptions of New York, Cape Town, St. Helena, none of which have any connection to each other and all of which essentially boil down to the pointless statement 'these are Atlantic cities because they are on the Atlantic ocean.")
Unsupported assertions abound. Apparently, musical instruments were not powerful enough before the 18th century to tackle the sea as a subject (whatever that may mean in the context of music). The "paramount" issue in the story of the Pilgrims is the Atlantic. What? How do you back that up? Even more bizarre, Winchester then undermines his own point by noting that it was important only as an obstacle to be crossed. Well, yeah. The Pilgrims are remembered for the founding of New England, not for their (total lack of ) seamanship or connection to the Atlantic.
Aside from the structural problems, Winchester's prose is often leaden and tedious. The opening story about his transatlantic crossing drags on for too long, pulls in totally unrelated issues like the meeting between Churchill and Roosevelt that resulted in the Atlantic Charter, and then peters out with no apparent point. As other reviewers have noted, almost everything is weighed down with vague modifiers. I suspect that these pleading modifiers are Winchester's unconscious attempt to make his lack of insight or, frankly, point sound "important."
Put simply, the book is a mess. The interesting subjects are covered in other books in better detail and with better writing. Winchester's writing about himself is dull and overwrought. Readers are better off sticking to books where Winchester has tackled a small, somewhat esoteric subject.