"Particularly pertinent to first-person shooters, strategy games, and casual timed or puzzle games, difficulty settings can mean the difference between an enjoyable experience and not being able to play the game at all. "
https://www.includification.com/cognitive/item/difficulty-levels
The AbleGamers Includification guide is a good read about implementing accessibility options in video games:
https://www.includification.com/AbleGamers_Includification.pdf