This is science fiction that I like. Your mileage may vary.
Try C. J. Cherryh. Almost everything of hers is technologically sound as much as a story needs (no lectures), has aliens and alien cultures that are truly alien (no Ukrainians in greenface), takes economics and politics into account (e.g. vast Union-Alliance future history), and you know what the protagonists know, no more. If you want something long, her First Contacts series starts with Foreigner, where the aliens have different instincts from humans and so contact must be limited to keep from inadvertently starting wars—and the humans are a small minority stranded on the alien planet. If you want a single novel, Finity’s End is good. Menyambal likes “Cherryh’s Chanur Saga. The spaceship’s captain and crew are female, for what that’s worth, catlike and dealing with multiple species.” I’d go for any of C. J. Cherryh, especially these series: Chanur, Exile’s Gate, The Faded Sun, Merchanter.
Also, try Connie Willis, especially her To Say Nothing of the Dog. And Fire Watch. And Impossible Things. And The Doomsday Book : real characters, real stories, and mostly happy endings.
I also recommend anything by James Tiptree, Jr. (Alice Sheldon). There’s a lot of alienation and a sprinkling of weird sex.
A mostly forgotten novel that I loved was Brian W. Aldiss’s The Dark Light Years. It’s about one man who finally learns how to talk to the aliens, when no one cares about them any more.
How could I have forgotten to mention Tanya Huff, a gay author of both hard SF (including some military SF) and fantasy. The real fantasy element in her stories is not the elves, it’s that whenever a gay character makes a pass at a straight character, the straight one is intrigued.
Look for the Year’s Best SF, xxth edition, which has been going on for about 25 years so far. You’ll meet new writers, old favorites, Hugo winners, etc. Try second hand stores or thrift stores or your local library. They’re hefty hardcovers.
Somewhere I have a paperback, Science Fiction Hall of Fame, Volume II B, which is so-o-o geeky! It’s full of good stories, all right, but “Volume 2B”? 2B? Nerds.
Remember also Barbara Hambly’s logical fantasy novels, which are continuous action from the first page. In fact, she seems unable to insert a phrase such as, “they rode north for a week,” instead driving her characters without rest from one ambush to another. Although I feel sorry for her exhausted protagonists, I like her work, which is colourful, imaginative, and logically consistent. She has an Unschooled Wizard series, a Dark Mage series, a Kingdom of Darwath series, and a pair of vampire novels set in Victorian times (Those Who Hunt the Night and Travelling with the Dead). There are other works, but those are the ones I like best.
Menyambal recommends “T H White’s Mistress Masham’s Repose. I dunno if it is online, but find an illustrated copy, read it, and pass it on to a nerdy child. Funny, English and full of life–away better than Harry Potter” and adds “Gutenberg has a marvellous selection of books in various file formats. Mostly older, but you can’t go wrong with Twain.”
Diverging into mysteries, also try Josephine Tey’s mysteries, especially The Daughter of Time, I think there are seven in all: The Man in the Queue, A Shilling for Candles, Brat Farar, The Singing Sands…