Scripts by the biggest science fiction writers of the day
This was really the exception, yes there were a few scripts by such, but other times it was just story ideas. The majority of Trek writers weren't big scifi novelists.
Pushing the outer edge of diversity
More (at best) staying up with the standard diversity of the media of the day. In many ways Trek fell behind society, and either had to play catch up, or simply didn't try.
Heroes whose limits are partly self imposed
How would this be different than a cop show, where the heroes are bound by regulations, procedural rules and legal restrictions? Plus the prime directive (especially in TNG) was a get out of jail fee card to exercise ethical/moral cowardice.
Trying seriously to portray people who had left barbarism behind
Kirk: "I will not kill ... today."
Trek (imho) was at it's best when it depicted average people in the future. Picard's condescending attitude to the side, there's not a single person in the 24th century who's better than people who can be found today.
There are good people and bad.
Characters who age realistically
As opposed to Jean Luc Picard, movie action stud.
With kung fu grip and optional dune buggy.
.