I'm neither a sci-fi nor a fantasy aficionado, and have only started reading these kinds of works here on Steemit. So... take what I say with a grain of salt. Like @jonknight, I like to not know what's coming. Suspense, in any kind of tale, is always nice. As for length, I am much better at reading short pieces. I hope to follow your writing adventure. Very exciting! Bottom line, you should write what speaks to you.