This book provided the foundation for most economic policy (in the west at least) through the middle of the 20th century, and as such must be considered among the most important books ever published. It will show the reader why certain decisions were taken, and how we got to where we are. Even if you don't agree with Keynes' theories this is an indispensable guide for anyone who wants to understand government economic policy.
Beyond his importance as an economist however, Keynes was a member of the Bloomsbury group of artists and Bohemians, and that is reflected in his writing. This is no novel, but there are few better written economic texts.