A lot of times I have trouble reading text in a game. I feel some developers prefer to be fancy, with bubbly text and outlines and bad letter spacing. It’s infuriating—I’m up against my monitor squinting trying just to process the glyphs on the screen as words and not “artful” pictures. If I cannot read your game I will not continue playing it.
Mabdulra, via Reddit

I love that dyslexia-friendly font. This is just amazing for someone like me. I didn’t have to read everything 3 times to understand every little bit of sentence. That is the exact reason why i gave 6/5 to your game.
Pyrophex, via Kongregate

Vision (basic)

For short passages of text, just an easy to read font over an unfussy background makes a big difference to readability, ideally a clean sans serif font with distinct letter shapes (e.g. no mirroring between p,d,p and q) and prominent ascenders and descenders.

Cognitive (basic)

For longer blocks of text, in addition to the above, aim for mixed case rather than all caps, unjustified left alignment, 1.5x line spacing, and around 70 characters per line.

There are fonts available that have been designed specifically for easy legibility. Some are designed specifically for dyslexia, but the principles used can also make them useful for some others who have difficulty reading.

Offering one of these can make a real difference if you have a text-heavy game, but if you’re using a more extreme one such as opendyslexic or dyslexie it should only be offered as an alternative rather than the single font choice, as they work well for some people, and make reading more difficult for others.

The Last Door offered a choice between a standard font and a dyslexia friendly font, and of the people who played through to completion, 14% did so using the dyslexia friendly option.

Best practice example: Lovers in a Dangerous Spacetime
Best practice example: Guacamelee!
Best practice example: Warlock of Firetop Mountain
Best practice example: Destiny 2
Best practice example: The Last Door

More information: Dyslexia-friendly typography (video)

Resource: FS Mencap (Commercial – premium)
Resource: Dyslexie (Commercial)
Resource: OpenDyslexic (Free)