@21 re "how much is too much". It comes down to what accessibility really is - the avoidance of unnecessary barriers that come between a player's medical condition and the experience the designer intended their players to have.

The key word in there is "unnecessary".

For a game to be a game it must have some kind of rules and challenge. If not it would not be a game, it would be a toy or a narrative. And any kind of challenge will be an impassable barrier for someone.

So games are by necessity and by definition inaccessible. Accessibility is an optimisation process, figuring out which of the many barriers present in any game are a necessary part of what makes it fun, or are in fact unnecessary barriers that get between the player and the designer's vision.

It is that dividing line that decides what is too much or not enough, and it varies from game to game. For example reliance on precise timing is a completely unnecessary and easily avoidable barrier in Civilisation. In Call Of Duty, not so much.

As far as multiplayer goes, the necessary / unnecessary thing applies still. There are three main strands to accessibility in multiplayer; firstly things that don't offer any meaningful advantage, like button remapping or colorblind options. Secondly things that reduce barriers at the bottom end without giving advantage at top end. For example auto aim; great for beginners, but too slow and inaccurate compared to manual aim for seasoned players.

Then lastly matchmaking, to allow people to for to play only with people who have similar preferences. Such as halo reach's "chattiness" preference, which allowed players to be matched up with other players who, in this the reach example, preferred to play with/without other players who had the same comms preferences.