In creative endeavors, like game developing, or painting, you can push further indefinitely in all areas of your design.
So how do you define being done? You have to choose to be done. There is no point in being done at a point where all areas are sub-par. If you feel that anything other than perfect is not good enough, you'll never be done. Perfect is an illusion, like the end of infinity.
Being outstanding, however, is very important. Outstanding means being noticeably interesting in relation to other endeavors. Being outstanding in all areas is ridiculously costly.
You can probably only afford to be outstanding in one, maybe two areas. Therefore, by reducing the total number of areas to a minimum, you gain the benefit of increasing the percentage of outstanding areas. You might even save enough effort to be even more outstanding in your key area.
So, decide on your key area, and polish its outstandingness from the start.
Now, it's time to start practicing what I've preached.