Studies in musical improvisation show that musicians and even children are able to communicate intended emotions to listeners at will. To understand emotional expressivity in music as an art form, communicative success needs to be related to improvisers' thought processes and listeners' aesthetic judgments. In the present study, we used retrospective verbal protocols to address college music students' strategies in improvisations based on emotion terms. We also subjected their improvisations to expert ratings in terms of heard emotional content and aesthetic value. A qualitative analysis showed that improvisers used both generative strategies (expressible in intramusical terms) and imaginative, extramusical strategies when approaching the improvisation tasks. The clarity of emotional communication was found to be high overall, and linear mixed-effects models showed that it was supported by generative approaches. However, perceived aesthetic value was unrelated to such emotional clarity. Instead, aesthetic value was associated with emotional complexity, here defined as the heard presence of "nonintended" emotions. The results point toward a view according to which the expressive content of improvisation gets specified and personalized during the very act of improvisation itself. Arguably, musical expressivity in improvisation should not be equated with the error-free communication of previously intended emotional categories.