So I suppose what I'm asking in a roundabout way is: what elements actually put the "fantasy" in "science fantasy"? What distinguishes it from science fiction?
It's mainly a question of atmosphere, isn't it?
Unlike fantasy, science fantasy is likely to:
- involve travel through space or to other dimensions
- favor "magical" effects that play on the fringes of what is scientifically plausible (psionics, hacking)
- avoid "magical" effects that completely override science/technology (esp. reliance on devices)
- strongly limit the scope of "magical" effects
To take Star Wars as an example, 99.999% of the population relies entirely on technology that is scientifically plausible. The jedi powers tend to be subtle, but even telekinesis and electrokinesis are explained in terms of the mind acting on a physical field that permeates space. Even the jedi need spaceships and life support systems.
To take the Barsoom series as another example, the entire population relies on technology. The only "magic" that most people ever see is limited telepathy. The only major exception is the city of people who can create mental illusions so convincing they can kill, and as a once-in-a-lifetime masterwork create a persistent mental construct. However, the science in that series hasn't aged well... while the power that keeps airships afloat might have felt plausible to readers when the series was written, it surely doesn't now.
Unlike science fiction, science fantasy is likely to:
- Favor character and quest stories over stories that explore the impact of technology on society.
- Give some characters a source of power that is independent of technological devices
This is just a quick attempt to write down some of the criteria that make up my own personal "I know it when I see it". I'm sure it's easy to find counterexamples.
But in my opinion, D&D is a poor fit for science fantasy mainly because too many character types rely on magic, there are too many different kinds of magic, and because there are so many spells that you feel magic can do pretty much anything. Science fantasy calls for a more "Grim Tales" approach (remember that book?!) where most PCs are mundane skill-users with equipment, but you might have one PC with powers.
To take another example, Shadowrun is pure fantasy dressed up in cyberpunk clothes. But if you removed 90% of the magic from the game, so the main "magic-users" were actually hackers, then you could run a good science fantasy game with the system.
Cheers,
Ben