“…good SF is usually about something (and often something very profound, such as whether or not God exists).” – Robert J. Sawyer
When I meet other authors, one of the first three questions I ask is “what is your story about?” (We can discuss the other two another time.) This generally turns into a description of the environment and the characters. Then I follow up with “That sounds like an interesting character/world/time/situation, but what is your story about?”
Let me expound on the difference. Lois Lowry could have described “The Giver” as “It takes place in the future. Every one is assigned a job for their entire life. One person can absorb all the memories from the people and there’s an old man and he’s going to die and pass all his memories on to a teenage boy.” When you read “The Giver”, you know that it’s about life being full of pain and joy, and Jonas’s loss of innocence as he discovers the human cost of freedom from pain.
How about a book about a military training ground in space preparing for a battle between humans and bug like aliens? This is an accurate description of “Ender’s Game” but Ender’s Game is about more. Ender’s Game examines humanity desire to destroy that which it doesn’t understand and the sacrifices we will make in the name of war.
World War Z (the book, not that terrible movie) is not about zombies.
Hamlet is not about a prince in Denmark.
You get the idea.
My own novel, Project Dandelion, is about the value of life. I try to examine the value of life from two wildly different cultures, mostly through the eyes of a young woman trying to define herself. One culture is from a world where life is cheap and expendable; one culture lives in a world where life is rare and precious. It just happens to be in future and on two different alien worlds. I could have written the same theme as fantasy or historical fiction or a horror book because Project Dandelion is not about space; it’s about life and death and love.
Now let’s briefly look at the problem with fan-fiction. An author writes a book. The book is about something say “self-sacrifice”. A wizard or robot or knight in shining armor gives up their life to save an enemy (hmmm… note to self…wizard robot knight…). Someone thinks Bobbo The Robot-Wizard-Knight is a cool character and so they write a fan-fiction about Bobbo. But the original story was not about Bobbo. The original story was about self-sacrifice. You end up with a story with all of the characters and environment but none of the meaning. Empty calories. Brain candy.
As an author (and as a thinking human), you have a unique perspective, opinion, and value system. Express those perspectives, opinions, and values through whatever genre you want but remember…Write Something That Matters
Write Something That Matters.