Though technically not essential, if you are good reader, you should have a good sense of timing, and be familiar with the nuances of the original piece. Eventhough many tunes are altered through the years, people like to hear familiar tunes. I am fortunate in being able to remember most details of the original recordings, and strive to duplicate them. Dynamics are also important, as well as tempo. Roger's submission "feeling" is perhaps the most overlooked.