Warren focused on the clarity of light and the structural integrity of his subjects. Whether documenting the ancient stones of the Propylaea on the Acropolis or the vernacular architecture of Yorkshire, his technique remained disciplined. He avoided the loose abstractions of his contemporaries in favour of a controlled wash that defined form through subtle shifts in tone. His views of Dorset and the high pastures of England demonstrate a keen eye for topographical accuracy.

Modern collectors value Warren for his ability to capture a sense of place without resorting to sentimentality. His watercolours provide a window into the late nineteenth-century travel experience, balancing the grandeur of classical ruins with the quiet charm of English villages. These prints offer a sophisticated aesthetic for contemporary interiors, providing a link to the intellectual traditions of the Arts and Crafts movement and the Harvard school of design.