Dillis is noted for his early adoption of painting outdoors. He frequently carried his sketchbooks into the Bavarian Alps and the Roman Campagna to record the specific effects of natural light. His watercolours and small oil studies avoid the heavy allegories common in the eighteenth century. Instead, he produced honest depictions of trees and local architecture. His work is defined by a sense of immediacy and a preference for informal compositions that capture a single moment.

Modern collectors value the work of Dillis for its spontaneous quality. His sketches often resemble the precursors to nineteenth-century movements like Impressionism. Because he avoided the stiff formality of his contemporaries, his art remains fresh and accessible for a modern home. His views of Italy and the German countryside provide a calm perspective on nature. These prints offer a connection to the origins of modern nature studies through the eyes of a meticulous observer.