First things first, I'm going to throw out five films that I think represent the narrative breadth of good science fiction: Star Wars (A New Hope), Sunshine, District 9, Aliens, and Independence Day. Clearly I'm leaving a lot of movies out, but that's inevitable. It should also be noted that I'm using a very broad and public definition for science fiction here, since Star Wars really doesn't count as true science fiction (it's science fantasy); but that's an academic distinction at this point, and not something relevant to the discussion.
So what is it that all five of these films have that make them good? It's not action, because Sunshine has very little of it. It's not the gritty, "realistic" feel of the films, because Star Wars very much lacks that. And, lastly, it's certainly not because of the presence of characters we can root for, because District 9 gives us a character who represents all that is selfish and terrible about humanity until the very end.
But that leaves us with an unanswered question. Are we simply drawn to the beautiful special effects? Are the plots what draw us in? Do we find the speculative elements most appealing, which are clearly lacking from non-genre productions? If it's the last of these, then we have to ask ourselves why we like some speculative elements and not others, which, I think, leads us to an unfairly subjective space that can't be argued out of (and, to be fair, all of this discussion is subjective, but at least something broad enough that we might be able to fairly address it). For me, I think it's a combination of the visual medium and the complexity or speculative power of the plot. What draws me into Sunshine is the sheer emotional power of what is going on, which is also the same thing that occurs with District 9. Independence Day and Star Wars are simply a lot of fun; yes, there's a deeper story going on there if you want to look, but what draws me to those stories are the characters and the situation, and how they both come together to produce good fun and character connections. But all of these things are varied and don't apply to every science fiction film I've enjoyed. I'm not so sure I can come up with a small list of criteria that links all my favorites together.
And so I ask you: what makes a good science fiction movie for you? What are you favorite movies and what about those movies draw you in?