Unlike recreational games, serious games do more than entertain the player. Serious games promote acquisition of information and skills that are valued in both the virtual world and the real world. The challenge is to design and develop serious games that simultaneously create an enjoyable experience for the player as the player develops or improves her skill set as a result of game play and applies these newly developed skills in a real world setting. Because transfer of learning represents the primary goal of serious games, it is crucial that game designers understand the interactions associated with game tasks and their impact on players prior to game development. Borrowing heavily from interaction design, we introduce the user centered game design methodology as the framework for serious game design and apply this technique to the evaluation of the social interactions between Player Characters in a commercial Massive Multiplayer Online Role Playing Game. Significant results from experimental studies suggest that this genre of games shows great promise as an unorthodox language learning tool for vocabulary acquisition and reveals the importance of social interactions in the virtual space of video games. Finally, we discuss the design implications for serious games that facilitate Second Language Acquisition.