What role does player feedback play in refining and evolving the art direction of a game during development?

Feedback plays a significant role in determining the final output of any game. Each and every aspect of a game should go through this phase for example Modelling, texturing, game mechanics, sound etc. All these parameters that make up a game should receive feedbacks. These feedbacks should primarily be from the client but you can also seek them from your collogues or friends to help you improve. 

While developing a game one can easily spend hours on one task and as a result can become vulnerable to even the simplest mistakes on the screen. Seeking feedbacks can resolve this issue.

Feedback also saves a lot of time in the game development as both the clients and the developers are constantly revised to be on the same page via these feedbacks.

So bottom line, give and receive feedbacks as much as you can during any project.