A good writer will you tell that the labels have shifted and blurred and it's hard to tell which one best describes the work most succinctly. But it is the blurring and blending of these genres that creates new, interesting work. Despite there only being two, or seven, or thirty-six fundamental plots, we as writers, can still satisfy the need for something new with the combinations of ideas and strong emotional cores for our characters.
It is important to have well-formed characters that your readers can empathize with--or viciously despise. It doesn't matter if your character is a child or a giant bug, characterization is characterization.
But the ideas are what make great fiction, especially speculative fiction. And no, I don't mean "Harry Potter, but in space! You're a martian, Harry!"
No, the best stories take aspects of the genre and make them integral to the story--not just parts of the proverbial stage.
Coming up with ideas that no one has seen before is tricky. At the very least, you need a fresh take on an old idea (again, not Harry Potter in space). Once you find that core idea, you can begin writing from there.