Today, Hemingway's style is one of the most copied around: it's gruff, it's stoic, and the sentences are shorter than the average length of one of Hemmy's beard hairs.
But way back when, his radical style (where were the poetic flourishes? where were the long asides? what did it all mean?) paired with the bleaktastic and jaded tone of The Sun Also Rises marked this novel as something new. Something, well, modern.
The book is seen as one of the big daddies of Modernism. It’s up there with Ulysses as shining examples of the genre and movement. Hemingway made a conscious move away from the conventions of the nineteenth century novel, attempting to create a new voice for the new world of the postwar twentieth century. The new world was stripped of excess sentimentality (like his prose) and filled with people that were lost and had pretty much given up hope of being found (like his characters).