As you point out, work is a relative term, but I tend to stick with its clearer definitions: doing something, moving something from one place to another. Thinking is work only if it leads to doing. One can have thousands of thoughts in a day, but where do they end up?
Reading is more work than watching a movie, IMO, because it engages the imagination. Writing is more work than reading because we have to find our own words, not just take in someone else's.
Because I think of work simply as action, I don't attach negative connotations to work and positive ones to play. Some work can be fulfilling and fun; other work can be drudgery. I'd rather do something that requires creative thinking.
Incidentally, this entry shares its title with a poem by Philip Levine.