Calli, CJ Cherryh does both fantasy and SF, both very well. Her plots are complicated, her characters deeply flawed. Stories move fast and generally everyone is injured, hungry, and/or exhausted for most of the action. Also under-informed, much like the reader.
She has a hugeass series of loosely-linked novels about human expansion, colonization, and cloning, called the Merchant-Alliance universe. The first of those is Downbelow Station, and it's as good a place as any to start: it won the Hugo and Nebula the year it came out.
Her Foreigner series is very popular, and is all about human-alien interaction, about alienation and cultural assumptions. That starts with Foreigner, I believe. Although those themes are ones she returns to again and again, for instance with The Faded Sun trilogy about a dying alien race, or Cuckoo's Egg or 40,000 in Gehenna or the Chanur series.
The Chanur series is pretty much straight space opera, told from the perspective of a grumpy female ship's captain who also happens to be, basically, a cat. Her crew takes in a creature they've never seen before, a "human", and get caught up in interstellar politics and intrigue about the possibility of a new species, and new trade openings. The Chanur stories are complex politically, but I find them less dense and more entertaining than the Merchant-Alliance novels, including Cyteen.
Rider at the Gate and Storm's Rider are what happens when a thoughtful and cynical writer like Cherryh takes on that classic trope of adolescent wish-fulfillment fantasy plumbed to such great success by folks like McCaffrey and Lackey. Telepathic animals in the same place as self-absorbed teenagers with raging hormones may not necessarily end in happily-ever-after...
Gate of Ivrel is Cherryh's first novel, the first of quartet of novels that read like fantasy wrapped in a gloss of science fiction. Morgaine is the last surviver of a team sent out to destroy the world gates, because they're too dangerous: they cross both time and space, and misuse is not only possible, it's guaranteed. She meets up with a very young man from a medieval culture, who doesn't understand anything of what she is or what she is about, except that she's very very dangerous... The Morgaine novels are great adventures, and I love the characters in them probably best of all of her characters.
Most if not all of these are in print, or you can find them at half.com.