Non-Free, Non-Fun
Now, if the goal of most video games are to please their users, to allow them to enjoy themselves to the best of their ability, it only makes sense to release those games as free/libre software. No matter how great a given non-free game is - in terms of technical or artistic achievement, innovation, and/or "fun factor" - it can always be improved by making it free. In fact, as a game developer, failing to do so conflicts with their obligation to please their software's users, and so represents an ethical contradiction. By giving users additional freedoms than are available for proprietary games, game developers can avoid this contradiction, improve the user experience of their games, and help promote a large, devoted, and welcoming gaming community.
Free software (in the "free as in freedom" sense of the term) must, by definition, give users at least 4 legal rights: the right to run the software for any purpose; the right to read and/or change the source code, so that it may perform any technically feasible task; the right to share exact copies, at no charge or for a price; and the right to share modified copies. (What is free software?, http://www.gnu.org/philosophy/free-sw.html) All of these freedoms are essential for gamers, for without them, their ability to fully enjoy their games is hampered.
The most important of these for computer games is the right to read and modify the source code of games. Many otherwise critically-acclaimed or popular games are noted for their inclusion of considerably annoying elements. For example, the Iron Boots in the legendary N64 game The Legend of Zelda: Ocarina of Time were widely criticized for not allowing users to remove them without pausing the game. Although Nintendo would later fix this flaw (more than 10 years after the original release of Ocarina of Time), allowing users to do it themselves would have allowed Ocarina's players to make the software more fun on their own. Moreover, since different players have different preferences, no non-free game can possibly satisfy all potential gamers, while free games can be modified to any player's tastes. A good options menu can be helpful, but any decision that seems perfectly reasonable to developers (for example, the 2-gun limit in Halo-series games) will inevitably displease some users. By controlling the rules of a game and preventing users from changing them, developers disrespect users and reduce the enjoyment those users derive from their games, but by giving them freedom, they ensure that any gamer can go his (her) own way.
This freedom is also essential for education in game development. As of 2012, more than X students enroll in game-development related programs in universities and colleges per year. In order to provide these students with the best possible education, and to prepare them for positions in commercial game development, they must recieve training in writing and modifying large, professional video games. A large supply of free games is essential for this task. Free games encourage learning, by allowing anyone to observe the algorithms and techniques used in them, and by allowing new developers to apply these techniques to their own projects. Non-free games reveal their source to only a chosen few, leaving all other motivated users lost, confused, and uneducated. Even those never intending to go into software development can potentially be interested in how a game produces a unique or intriguing scenario and wish to find out how it is done. If the game is non-free, their hearts sink as they realize the source is off-limits. However, if the game is free, they can look up the source and satisfy their curiosity. In short, by not making source available for their games, the developers of proprietary software violate the principle of maximum fun.
