Poems are highly complex aesthetic objects that vary across both objective stimulus features and subjectively experienced qualities. This study sought to determine which of a subset of subjective qualities-vividness of imagery experienced in reading, valence, and arousal of perceived emotion in a poem's content-most determine aesthetic appeal for two highly regularized genres: haiku and sonnet. Participants recruited online using Amazon's Mechanical Turk read and rated haiku and sonnets on four characteristics: valence, arousal, vividness, and aesthetic appeal. Our results indicate that individuals vary greatly in experiencing aesthetic pleasure, with high disagreement about which poems they found most appealing. However, across participants, vividness of imagery was the strongest contributor to aesthetic pleasure, followed by valence and arousal. While individual poems vary greatly in their appeal to individual readers, individuals generally agree about the perceived emotional valence of poems in both genres. This study also characterized a stimulus set of haiku suitable for further experimentation in aesthetics or emotion research.