As a digital learning medium, serious games can be powerful, immersive educational vehicles and provide large data streams for understanding player behavior. Educational data mining and learning analytics can effectively leverage big data in this context to heighten insight into student trajectories and behavior profiles. In application of these methods, distilling event-stream data down to a set of salient features for analysis (i.e. feature engineering) is a vital element of robust modeling. This paper presents a process for systematic game-based feature engineering to optimize insight into player behavior: the IDEFA framework (Integrated Design of Event-stream Features for Analysis). IDEFA aligns game design and data collection for high-resolution feature engineering, honed through critical, iterative interplay with analysis. Building on recent research in game-based data mining, we empirically investigate IDEFA application in serious games. Results show that behavioral models which used a full feature set produced more meaningful results than those with no feature engineering, with greater insight into impactful learning interactions, and play trajectories characterizing groups of players. This discovery of emergent player behavior is fueled by the data framework, resultant base data stream, and rigorous feature creation process put forward in IDEFA--integrating iterative design, feature engineering, and analysis for optimal insight into serious play.