Most computer games do not work well for gamers with only one hand. Try it sometime. Either the controls are spread all over the keyboard, playing the game requires the simultaneous use of the keyboard and mouse, etc, and many games do not have adequately customizable controls (if at all). Including customizable controls with both mouse and key bindings for everything would go a long way toward solving the problem. I put my trackball on the left side of my keyboard (my right hand does not like to behave) within reach of the leftmost keys and then, if I can, bind important controls to my four trackball buttons and the keys on the left side of the keyboard. I actually manage pretty well that way in WoW, but it's far from a perfect solution, and a lot of games are not that customizable.
There are gadgets and special controllers, but they are usually specialized and not meant for cripples, and not very well designed in the first place.
This leads me to ponder minimal and flexible UIs, both for cripples and other people. Ring menus come immediately to mind. They are like mouse gestures but don't require as much coordination and give visual cues instead of having to memorize gestures (also a problem with keybindings). Also they can be accessed with the keyboard. Speech controls are another option - even "mutes" are able to grunt. Eye tracking is also surprisingly easy with a cheap "webcam." And of course different inputs can be used together. Most game UIs need to be able to "point" and accept atomic commands. That's really not too hard and does not need complex or specialized controls.
Also, many games have ridiculous things like, for RPGs, having to click on individual containers to loot them. Why not just have a command to get a menu of all the loot in range? Is there really any value to making players have to sort through a pile of corpses? Same with selecting things in a cluttered environment: if I click near a collection of dense targets the game should give me a ring menu to select which one I mean instead of making me hunt for the right pixel.