In the example you used :
Movies are fun >>> Les films, c'est chouette1.
Why? As a rule of thumb when refering to categories or sets :
The whole set (all movies) >>> les films
Multiple objects in the set (some movies) >>> des films
Of course, here it's not a logical statement where you would refer to a whole category and really assert that ALL these movies are equally fun. In casual speech it'll be a way to refer to movie-watching as a fun activity rather than saying anything about any or all movies being fun.
Using no articles at all does not occur outside of poetry and literature contexts, or maybe in very rare cases that don't cross my mind at the moment but it must be anecdotal, if any.
1 I changed the structure a bit to make it sound slightly more natural to french ears, but it changes nothing to the very point of your question nor to its answer, in my humble opinion. If you find it confusing, I'll change it back.