Ok, so given that it's hard for gamers to broadly define what sci-fi is, it's worth calling out a pair of sub-genres which have managed to escape this problem.
First off, Cyberpunk is recognizably its own thing. While it has many influences, and even a few flagships of its own, the idea has never cemented into a single vision. There are trappings which recur (the net, cyberware, corporations, suburban visions of urbanism and such) but exceptions also abound, especially where the boundary between cyberpunk and "near future sci-fi" gets fuzzy. What's curious about Cyberpunk is that I think it's benefitted a lot from competing yet overlapping visions. This is as true of the source material (say, Gibson vs. Sterling) as it is of the gaming material (Cyberpunk 2020 vs Shadowrun, say). Where the split between Star Wars and Star Trek leaves only a small amount of overlap, cyberpunk material swims in the same pool, but it's a varied enough pool that it's not disruptive when a specific example reveals the thing that makes it different (like biotech, aliens or magic). This is kind of cool, and it explains why an idea which is basically a past vision of the future remains so potent for us.
The second big genre is military sci fi. In books, this is a huge swath of stuff, and it has lots of recurring elements. There's actually less gear porn than you'd expect, but also a lot more politics. If there's any one thing that keeps military sci-fi from being coherent it's that the particular ethos that the specific tactical genius of that particular series endorses is such a moving target. The weird thing, however, is that this is not something that's made a lot of transition into gaming, which seems odd, because the trappings are definitely a good match.
I think there are two big factors at work here. First, if this is your genre, there's a god chance that you can just play GURPS and be happy with it. There are a lot of assumptions baked into that statement, but I think there's more than a little truth to it.
Second, and perhaps more importantly, I have very rarely seen military sci-fi structured in a way that I would consider group friendly. The role of the protagonist - usually a military genius isolated and unrecognized because of [shortcoming that is a problem in the setting but which we, the reader, think should not be held against them] - is also the role of commander. Other characters might be important, but they must either be subordinate (bodyguards, soldiers and the like) or outside of the world that important things happen in (love interests and politicians, mostly). Not to say you can't come up with a group for play in many of these settings - it's easy to do - but doing so requires you do something different than follow the normal shape of the fiction.
I should note, I'm sure there is some military sci-fi out there that doesn't follow this model - it's just that I've seen it so often that I kind of view it as baked in. If you've got a counter-example, then run it through this metric. How many strong relationships to characters have to people other than the main character, and how static are those? There will always be some - people have families and the occasional romance - but they aren't particularly robust or fiction-driving, at least beyond their establishment. This is not a criticism of these books - I loves me some Vorkosigan - but just an observation on how they're structured.
Now, as I thought about these things, it occurs to me that there's a third sub-genre worth noting because it's possible that it won't be overwhelmed by its media, and that is of course the small, diverse ship crew working to get by. This is Firefly, certainly, and it's a large swath of Traveller, and it's going to be a big part of Bulldogs too, an dit probably needs a pithy name. It's is an oddball because, to be honest, if there are books about this then I have not read them (and I'll happily take suggestions). Maybe that means it's not really even a sub-genre, it's just a stump. Maybe it really just is the "Firefly" genre and that's all there is to it. I honestly can't tell from this vantage point, but it will be curious to see if this grows into its own thing, or if it's just a cul de sac.