Are science fiction languages different from fantasy languages? I think they are, at least to some degree.
People think differently when they invent languages for fantasy and science fictional societies. When someone sits down and thinks about a fantasy society, very often they're thinking about it from the insider's point of view. They're going to be putting characters in this world and you'll be on their side, wanting to feel close to them. Therefore the language tends to have more familiar, friendly features. For a science fictional society, very often people are thinking, "aliens!" Aliens are outsiders. That means that typically, languages designed for science fictional societies are more prickly. Harder to pronounce, and more off-putting. The most extreme examples are those from early science fiction where the words are all consonants just for the sake of making them hard to pronounce. Vxklrp! (I made that up.)
Of course, there is a continuum.
(I'm currently writing this from my parents' house, so I don't have a pile of books with me where I could go fishing for examples. If there's interest, I could return to this question again at greater length with books in hand.)
My gut says that fantasy languages are more likely to resemble English and to have English-friendly meter and onomatopoeia - or to resemble languages which English speakers regard as friendly or parental, like Spanish or Latin. Science fiction languages are more likely to go farther afield into the alien territory.
Here's the critical element: authors make these choices. They choose the "feel" they want their constructed language to have, and how extensively they want to create its structure and vocabulary.
An author who knows a particular non-English language would surely be inclined to use that language as a partial basis for a constructed language. Tolkien used Finnish as a basis for Quenya, the High Elvish tongue, and Welsh as a basis for Sindarin (Grey-elven). I think this is a great idea. Na'vi was designed to mesh features of different Earthly languages including native American sounds so that it would be very alien, but sound accessible.
Both the Elvish and Na'vi languages distinguish themselves by having extensive structure and enormous vocabularies. That's not something that necessarily differs by genre - that one differs based on how the author intends to use it. If you've got a movie you're working with, that automatically requires an extensive vocabulary, because people have to speak it. By contrast, most languages for written stories don't need such a huge vocabulary. Tolkien got away with putting whole foreign-language stories and songs into his books, but not everyone can (or should) try to do that.
Do I have any message that might grow out of this for writers and works in progress? I suppose it's that you don't have to make your constructed language follow these trends. Think it through. A constructed language doesn't have to have a really extremely alien feel to be workable for a science fiction context. It doesn't have to feel super-friendly to be usable for Fantasy either.
Ask yourself: what flavor do I want this world to have? How accessible do I want it to feel to readers? If you want it to be accessible, try having the words of the language be pronounceable by humans - this is not just a problem in science fiction contexts, but fantasy contexts too! Oh, how many times have I heard people say, "Why do authors insist on giving their characters names I can't pronounce?" Try out the words on your own tongue.
Here are some of my own examples. All of my stories tend to include the language of insiders, so the names and words tend to be pronounceable.
With Varin I try not to use much translated vocabulary, and I'm very careful to keep most names (especially first names) short. Tagret. Aloran. Tamelera (that's one of the longest). Garr. Reyn. Gowan. Fernar. Karyas. Selemei.
Khachee is a bit more complex because of the otter sounds I based it on, but I try all the words out myself. ChkaaTsee, TsorrPfirr, Cochee-coco.
Aurrel is growly and I always imagine it to have more interesting guttural sounds than appear on the page - but readers don't have to imagine all the sounds I do. Ru-rulii, gharralli, molri.
Despite my science fictional/linguistic bent, I don't tend to like making languages that are so foreign my readers can't stretch their mouths around them. It's because I like to be friendly! And also because the insider perspective is the one that appeals to me as an anthropologist.
What do your languages look like? What are they for? Shall we talk about it?