One of the most frequent arguments for deploying serious games is that they provide an engaging format for student learning. However, engagement is often equated with enjoyment, which may not be the most relevant conceptualization in safety-critical settings, such as law enforcement and healthcare. In these contexts, the term 'serious' does not only relate to the non-entertainment purpose of the game but also the environment simulated by the game. In addition, a lack of engagement in a safetycritical training setting can have serious ethical implications, leading to significant real-world impacts. However, evaluations of safety-critical games (SCGs) rarely provide an in-depth consideration of player experience. Thus, in relation to simulation game-based training, we are left without a clear understanding of what sort of experience players are having, what factors influence their engagement and how their engagement relates to learning. In order to address these issues, this paper reports on the mixed-method evaluation of a SCG that was developed to support police training. The findings indicate that engagement is supported by the experience situational relevance, due to the player's experience of real-world authenticity, targeted feedback mechanisms and learning challenges.