To me all the design disciplines (systems, gameplay, UX, level, narrative) have two facets. One is the vision and the other the content.
The vision is always what interests me the most. I believe that games are a synthesis of certain fantasies. They have their structure in terms of mechanics, gameplay, win/lose conditions, and so on. But this structure serves the purpose of delivering a vision.
The content is fun to produce. Creating levels or scripts puts me in a flow state, I can spend hours without even noticing it. Especially certain tools make everything so much fun. The content serves the vision above and should be always checked under that lens.
I think that the work I do is juggling with these concepts every day, every week, every month.