The following list is ordered from greatest to least, in approximate difficulty and quality. I include general information about the novels, as well as tips for how to approach them. All are modern works of art and will completely change how you look at writing. A few are shorter and less complex; others are leviathans.
1. In Search of Lost Time by Marcel Proust (1922)
Words feel inadequate when it comes to describing the ability of Proust. He is a giant. He went almost his entire life without publishing much of anything, and then during the last several years, wrote an over 4,000 page semi-autobiographical novel, split across seven volumes. The result was unlike anything seen before or since. In addition to completely reinventing the form, In Search of Lost Time was the first novel to openly approach the subject of homosexuality.
Proust was an artist and an intellectual. He made no substantial profession out of writing, it was his passion. True to promise, this is the most difficult work on the list, mainly for the scale of its architecture. Be prepared to read beautiful, fluid sentences strung together by chains of subordinate clauses and digressions, some going on for over a page. The narrative is non-linear and travels through time seamlessly. There is a learning curve, but it pays off.
The reward? It’s the greatest novel I’ve ever read. There is no other writer who can constantly evoke universal truths of human experience in writing, with a style so artistic and emotionally deep.
“Happiness is salutary for the body, but sorrow develops the powers of the spirit.” -Marcel Proust, In Search of Lost Time