Thought provoking morality plays at its best, solid SciFi when its mediocre.
What the writers of the shows say is so special about Star Trek: Its a superset - you can pretty much write with every episode a new story in another genre for "Star Trek", while most other shows pretty much repeat a formular in variations every episode.
I personally think, its a very interesting mix: Showing the evolution of the culture of empathy (beginning with Sokrates and Kant) by easy to understand/follow stories to teach the values of empathy like the old fairy tale morality plays of Grimm do for kids, set in the future to disconnect the content from contemporary cultures, mixing international cultures, using a modern form of story telling. The meta structure of "Star Trek" spans from the past into the future to reflect about today on a global scale.