One of the most rewarding aspects is continuing great relationships with people as well as making new ones and always trying to be better each new day - Seize the Day!
I think finding a job that will give you new challenges every day is really important! This will help you feel very engaged in your role, and challenge you intellectually. Another important aspect is working for a company/industry that you feel very connected too. This will help to motivate you when you are going through challenging times in your role, if at the end of the day the you are passionate about the company's mission.