Robertson's reputation rests on his series of plays for Marie Wilton's company at the Prince of Wales's Theatre. They were seen as "problem plays", because they dealt seriously and sensitively with social issues of the day. "Caste" was about marriage across the class barrier and "Society" explored prejudice against social mobility. The plays were notable for what the critic Thomas Purnell dubbed their "cup and saucer" realism, treating contemporary British subjects in settings that were recognisable, unlike the oversized acting in Victorian melodramas that were popular at the time. The characters spoke in normal language rather than declaiming their lines. Looking back thirty years later at the original production, Bernard Shaw called Robertson's play "Caste" "epoch making ... After years of sham heroics and superhuman balderdash, "Caste" delighted everyone by its freshness, its nature, its humanity".