What are the characteristics of romantic novels?

Your question may refer to two styles of writing- romantic fiction or novels produced during the Romantic Period. I will describe both.

Romantic or romance novels focus on the story of a love relationship, typically between two people. This relationship is what ties the story together-- it creates continuity in the plot. In addition to a central romantic relationship, romantic novels ought to have an "emotionally satisfying or optimistic" resolution. Even if the characters face many hardships in their relationship, even if one dies, a romantic novel will tell a story where love wins at the end of the day.

Romantic literature, or that produced during the Romantic Period, describes a style of writing which flourished in the first half of the 19th century. Romantic Period novels are characterized by rich use of emotion and sensuality. Many novels written during this Period emphasize individual feeling and deal more with the emotional consequences of the story as opposed to a more "cut and dry" relation of events.