The first thing I remember reading in this short snappy novel is its first Library of Congress Subject Heading. These types of headers are published in every novel catalogued by the U.S. Library of Congress (I'm assuming international readers aren't as familiar with them, but maybe I'm wrong - anyone?). I like to check them out to get a sense of a novel's themes, locations, and characters -- and because I'm a big nerd. The first subject heading tag read: "Middle-Aged Men -- Fiction." Not the most effective way to catch my attention.
Luckily, I read more. In fact, I read the entire book in one sitting because I couldn't put it down. The story itself was simple enough. In fact, the entire plot can be (and is) reduced to a single line of equation about 2/3 of the way through the book. But the way Barnes related the story, intermingling the main character's reflections, gave the story a powerful emotional charge. The bisecting of the story into two unequal parts was very effective, and I'm sure you can look to any number of other reviews for some truly fantastic snippets of quotes on memory, self-delusion, and storytelling. Once through the first time, I realized that I had probably missed picking up on an enormous number of tiny clues, and literary moments that would make a re-read thoroughly enjoyable. I will definitely read this book again.
Overall, I agree that this was perhaps not a "major" work - it was not an epic, it did not effect a major change on the way I read or see the world. But it was a thoroughly enjoyable, intelligent, and compelling novella. This win reminded me of the win of Ian McEwan's Amsterdam - another great little novel by a well-deserving author, and I'm not sad that it won.