The design of serious games for learning is shaped by a fundamental tension between realism and abstraction. Realism in serious games can manifest in multiple dimensions, such as graphical fidelity, sound design, game mechanics, narrative structure etc. Some serious games aim for high-fidelity simulation, replicating real-world scenarios as closely as possible (e.g., flight simulators or medical training applications). Others may incorporate abstract elements while still being grounded in real-world principles, such as strategy games that simplify complex decision-making processes. Abstraction, by removing unnecessary complexity, may reduce extraneous cognitive load and enhance generalisation of learning. In contrast, realism may support situated learning and contextual skill transfer, particularly when training requires familiarity with real-world environments. To better understand the implications of abstraction and realism in serious game design, this paper comparatively explores two case studies: FLIGBY, a corporate leadership development game Cipher, a languagelearning game designed for children. Findings identify six key dimensions that differentiate abstraction and realism in serious games: visual style, audio style, mechanics and interface, rule systems and feedback. Engagement, motivation and cultural perception are also considered, noting that realism may appeal more in professional settings, while abstraction may be particularly effective in child-centred learning environments. This research contributes to the broader field of serious games by providing a conceptual framework to guide educators, game designers and researchers in making informed design decisions, also offering a foundation for future empirical research.