Nels Anderson @ Gamasutra: "Last week, I claimed that game readability can be improved with increased emphasis on empathy and data. I'll be discussing the importance of the former first, but there's quite a bit of overlap between the two.
I neglected to offer a solid definition of readability previously, so I will correct that now before we progress. Consider readability to be a measure of the player's understanding of what outcomes are possible and how they can affect those outcomes. Basically, the inputs and outputs of the game's systems.
We can distinguish this on both a micro, minute-to-minute level and a macro, long term level, but it's the case that problems in one often affect the other."