I was thinking about why it was that generic scifi games don't really work. The problem is only compounded in games that purport to be rules-light. When compared to the success of generic fantasy games, the question becomes positively glaring.
Why can't there be a scifi game that's both light on rules and not tied to a particular setting? Oh, and that doesn't suck.
I recall when the original 3BB version of Traveler came out, and I occasionally see that mentioned as a "generic" scifi game. But no; it still has a bunch of assumptions built into it about the setting. The "vaguely Imperial" setting. The races. The technology. FTL drive. Social structure. Economics.
Is it perhaps a function of the fantasy genre that designing a game that is broad enough to incorporate all of the fantasy tropes is relatively easy, compared to scifi? After all, fantasy has its basis-- at least broadly-- in real history.
Everybody knows what a sword is, and a sword in Lankhmar is the same as one in Aquilonia, or Furyondy, or Waterdeep. But what is a blaster? A blaster in Star Wars might be very different than a blaster in Flash Gordon. So a scifi game must, perforce, define what a blaster is and how it works, and in doing so might cut out a particular use of the term in some other milieu, unless one resorts to endless variations encompassing every possibility, or resorts to sticking with a specific setting. In the former case, it's no longer "rules-light" as far as I'm concerned, and in the latter, it's no longer generic.
Consider, for example, the problem of designing a game that could cover Conan, Fafhrd & The Grey Mouser, Elric, Lord of the Rings, and Harry Potter. The original D&D game could, I would argue, do that. A few tweaks here and there, adjust some spell lists, and voila! It would work. Hell, they had rules for Conan, Elric, and Nehwon in the original A/D&D rules!
Imagine a game, though, that could cover Dune, Star Trek, Star Wars, Terminator, and the Foundation Trilogy. GURPS might manage it, with a separate world-book for each setting. But there goes the "rules light" idea, and probably the "generic" idea as well, since it would turn each into it's own sub-game with its own special rules. Even Star Trek, arguably a genre unto itself, needed separate games for different time periods, as Unicorn Games ended up doing it (a fine game line, I might add). But it was all very setting-dependent. You couldn't use it in a "generic imperial" setting without completely reworking it. You might as well make a new game. But whatever you came up with wouldn't work in a post-apocalyptic setting, or a Transhumanist near-future setting, or Babylon 5.
I would argue that science fiction is simply too broad to allow a single game system to encompass it all. Fantasy (pulp, high, or swords-and-sorcery), which by its nature is based at least somewhat in history, has a coherent and somewhat well-known background upon which to draw. Science fiction, which is much more speculative by nature, doesn't afford that same comfort. What's a blaster? What's FTL drive? How do psionics work? Do they even exist?
I've long looked for a rules-lite scifi game that didn't come with any pre-prepared background. I'm coming to the conclusion that it's just not possible. You either have a background that limits your options, or you are forced to accommodate so many options that it's no longer rules-lite.
Or am I just missing something completely basic?