For me what defines science fiction is whether there are questions being asked - questions about the world in which the story takes place, and also questions about our world. Sci-fi to me is SCIENCE fiction, which means it adheres to the tenets of all science - namely, searching for answers; coming up with solutions to problems and seeing if they work. They can be huge problems or little problems of just one person, it doesn't matter. Hard, soft, flavoured with romance or noir, I honestly don't care. Asking questions about physics, biology, linguistics or politics, or even how one small change would affect humanity's existence - again, I don't care. It's just gotta be asking something, because if it ain't asking questions, it ain't SCI-fi.
That being said, the primary driver of those questions is the characters, so they characters HAVE to be well-written, or you're missing your "FIction" part of sci-fi. So often you see people lauding some work of science fiction for the science bit, but the characters are as engaging as the dummies they use to test pedestrian detection systems in cars - vaguely resembling a human shape. Yeah, no thanks.
I read a pretty wide variety of stuff - Asimov's Nemesis is an old favourite (couldn't get into Clarke). I also really like Record of a Spaceborn Few by Becky Chambers, Phoresis by Greg Egan, The Dispossessed by Ursula K Le Guin, Downbelow Station by Cherryh, and Snow Queen by Joan Vinge. I think the only sci-fi stuff I don't enjoy is the mindless action stuff - it doesn't do well in books since the action is so abstract. Just not really fun to read.
My own comic is about a young girl who flies off to space in search of answers about an old spacer myth - the Fable of the Wandering Planet. She believes that this planet will give her answers about why her mother - and a famous deep space captain - had disappeared. Am I gonna nail all of my own expectations? Errrr... doubtful. But I'm gonna try anyways.