This document discusses game user interface (UI) design and immersion. It provides case studies of Far Cry 2, Dead Space, and Team Fortress 2. Far Cry 2 aimed for a fully diegetic UI but struggled with balancing immersion and functionality. Dead Space used diegetic holograms and player avatars to render interfaces atypically while preserving functionality. Team Fortress 2 mixes UI styles without a consistent theme but largely succeeds through prioritizing information delivery over immersion. The document advocates balancing immersion and functionality, as diegetic interfaces can reinforce fiction but are difficult to design properly.