Elves, magic, swords and the like combined with an in-depth story are a wonderful treat. There’s something very appealing to that. At the same time, I love stories about the future, space travel, time travel, dystopian societies and/or alternate realities. The thing about science fiction is that it can encompass pretty much all the fantasy genre can and more, which is why I like science fiction a bit more than fantasy, though I love them both.
Science fiction can incorporate fantastical elements such as swords, ‘magic’, and elves easily within the genre. They just might require a different explanation than the fantasy genre offers for their existence. The entire story can take place without any lasers, any spaceships, or anything you might normally associate with the science fiction genre. It could take place on an imagined planet with different environmental elements (such as a binary stat system) which affect a society on the planet, as in the book trilogy, Helliconia, by Brian Aldiss
. Or it could have all the elements more commonly associated with science fiction. Possibilities seem wider in science fiction to me, though fantasy can definitely incorporate some interesting twists.
I think fantasy does a lot of the same things as science fiction, but with a different feel/perspective to it. Majora’s Mask, depending on your perspective, can be said to incorporate a bit of science fiction in it with travel to a parallel universe. (This could also be painted in the light of fantasy, with it being a magical portal.) Time travel in Ocarina of Time is done in a more fantasy way, using a magical instrument. Whereas time travel in science fiction is done with more, yet less, (Since it obviously isn’t explained in maximum detail) explanation in the ‘how’ of time travel. Science fiction and fantasy are close in these kinds of ways, and I love them both. Given my current exposure to either genre I do tend to favor science fiction more though.
In terms of the gameplay, you could have either storytelling genre/setting in pretty much any gameplay genre, so I’d have to know that genre to rate them in that context.