The paper discusses two different approaches in designing and evaluating serious games: games as inputs in non-game activities, and games as modulation of non-game activities. Playing and gaming offer powerful metaphors and interpretive repertoires for making sense of professional challenges: for example, business and politics may be seen as gameful, while computer engineering may be seen as playful. Serious games are uniquely positioned to support or modify such repertoires, turning them more or less competitive, collaborative, exploratory, rule bound or rule bending etc. Their modulation force thus becomes a distinctive topic of evaluation. We discuss a case study illustrating how a successful assessment of a serious game seen as input for educational activities has obscured its ambivalent modulating influence on creating a playful take on computer engineering. Common glosses of serious games as ‘competitive’ or ‘useful for learning’ may divert attention from the relationships between specific game features, such as a particular organization of competitions and score display, and play styles. A successful translation of game playing into a desired professional ethos depends on fine-tuning relevant game features and game related discourse.