Changeable Font Sizes
Since the invention of text and graphical displays, one of the most basic options has been the ability to change the size of text. However, video games do not often provide the option. Gamers with visual difficulties including those that are legally or almost totally blind can still participate in many games, but reading text in the subtitles, directions/instructions and chats can be frustrating if the size of the text is just barely too small to read.
One example of a game that does this well is EverQuest II, which allows users to change text size.
Text size matters to more of your audience than you might think. Up to 50% of the aging gaming population has or will have vision problems in their lifetime.
A man loves playing an online adventure game, but his eyesight is slowly fading as he ages and his macular degeneration continues. He squints at the screen with the most powerful glasses money can buy, but the text continues to be harder to read. If the game allowed him to increase the size of the text in his chat window and on quests, he would be able to continue playing the game without interference.