I have played what the makers claim to be "the world's most inaccessible game" - Game Over!. I think it was the second game in six months time that I could actually play on my Linux platform which is a bit ironic. Anyway - the game was made by "Universally Accessible Games" a research project in Greece and it's a space invaders clone designed to illustrate several guidelines and principles one should follow to make a game as accessible as possible. As you might have imagined it does this by violating these guidelines. It is fun to play in it's own way. Even though starting the game is probably the very best part of it:

Press the following shortcut to start:
Ctrl + Shift + Enter +Page Up +F3 + F12 + Right Arrow

The thing is that most of the principles presented should already be pretty obvious to anyone making a game. No - you shouldn't write the instructions in Swahili if your players don't speak it . You should write them in a form that's clear and easily understandable for everyone. Everyone gets that, the difficulty lies in the next step - how to achieve just that.

Other principles are hard or almost impossible to implement in every game, like this one: "provide control over game speed". There are lots of games where the speed of the game are such a big part of the core design that you can't have the player adjusting it without major impact on the design. Not even mentioning online games where the speed necessarily have to be the same for everyone playing it.