A playability concern is when the design of a system hinders use of the system or the game as a whole.

A bad interface, overly complex syntax, poor or misleading instructions, or systems that don't provide you sufficient resources meaningfully use them - these are all examples.

A good example of a playability driven decision is the fact characters with social outrage/corruption can still withdraw money.

You can have a system that is perfectly playable, but not fun (usually because it's boring and unengaging). On the other hand it's hard to have a system that's fun that also has poor playability (This tends to result in frustration).

-Raesh

"Ever notice that B.A.'s flavor text swells in direct proportion to how much one of our characters is getting screwed?" - Brian Van Hoose