Sci Fi is tough... so many are series. Every time I want to revisit the Sci Fi genre I have to wade through dozens of Series, or sagas varying from 3 novels to who knows? Some over 20 books! It's hard to find stand-alone Sci Fi. FORTUNATELY, for me... I much prefer hard Sci Fi than the other genre of Sci Fi... 'fantasy' if you want to include that. And in Hard Sci Fi it's a bit easier to find stand alone novels.
It's not that I don't like series... but I am picky and it's very few saga's I have begun AND finished... so I tend to stay away from them... which means I'm probably missing out on some great reads. - JamesJM