Science Fiction

Ilium and Olympos by Dan Simmons. Combines post-apocolyptic dystopian earth, Greek mythology, man-made AI robots that have left earth, and the Trojan War all together in one story, although complex. Bit of a fantasy vibe in there, but it's all tied together based in Sci-Fi. Masterpiece of writing, IMO. If you liked his Hyperion books you'll love this duology.

Armor by John Steakly. Pretty intense read about a soldier with advanced body armor in a very long, drawn out battle with an insectoid alien race.

Temporary Duty by Ric Locke. Aliens make peaceful contact with Earth, and the navy ends up sending two recruits as advance team aboard a merchant ship. Turns out even advanced alien races have stuff to learn from Earthlings. It gets to be a kind of a self-serving fantasy, but it's a pretty fun read. Sadly the author died before finishing the sequel.

Old Man's War by John Scalzi. In the future after mankind became an intergalactic civilization, for some unknown reason the military is exclusively recruiting seniors of retirement age to enlist in the military and start a new life off-world, to never return to earth.. No one knows exactly what that entails, but widower John Perry decides to enlist after he turns 75. He finds out firsthand why they are recruiting the aging population, and the terrible secrets that have been kept from everyone on Earth.

And of course The Expanse Series by James Cory. Well known nowadays with the successful show, just a realistic portrayal of how the future of humanity may pan out, with some alien influence along the way.

Some of my favourites:
Murderbot series by Martha Wells
Imperial Radch series (Ancillary Justice/Sword/Mercy) by Ann Leckie
Vorkosigan Saga by Lois McMaster Bujold
Dogs of War duology by Adrian Tchaikovsky
The Expanse series by James S A Corey
Monk & Robot series by Becky Chambers

I've not read the Xeelee series so can't say if there's any similarities, but they are all excellent sci-fi series and well worth your time.

Love the Expanse (who doesn’t?), one I really liked is the Silo series. It’s not based in space so a bit different to the ones mentioned.

I love all the classics posted like dune and brave new world etc but I read Children Of Time last year and it blew me away. Couldn't put it down. Highly recommended

I love the Broken Earth trilogy. I appreciate how it shows different kinds of people and species creating forms of kinship different than the prevailing modes of kinship in the story's setting. It reminds me a lot of The Parable of the Sower, which is another favourite. Also, the orogenes and how they interact with both natural and human made structures is very cool!

I’m really enjoying everything Martha Wells is writing about murderbot!

I slept way too long on Peter Watts and Ted Chiang. Both recent new faves

Big question...

Kim Stanley Robinson - Mars Trilogy, Science in the Capital series, Antarctica
Neal Stephenson - Anathem, Snow Crash, The Diamond Age
Ken MacLeod - Fall Revolution series, Execution Channel
Robert Heinlein - Podkayne of Mars, Moon is a Harsh Mistress, Starship Troopers
Sean McMullen - Greatwinter series
Joe Haldeman - The Forever War
Connie Willis - Doomsday Book
Ursula K. LeGuin - The Dispossessed and The Left Hand of Darkness
William Gibson - Neuromancer, The Bridge Trilogy, and the Blue Ant books
Iain Banks - Consider Phlebas
Samuel Delany - Dhalgren
Maureen McHugh - China Mountain Zhang
Nicola Griffith - Ammonite
Pat Murphy - The City, Not Long After
Frank Herbert - Dune
Arthur C. Clarke - Childhood's End, Rendezvous with Rama
David Brin and Gregory Benford - Heart of the Comet
David Brin - Startide Rising
Walter M. Miller, Jr. - A Canticle for Leibowitz
N. K. Jemisin - The Fifth Season
Charles Stross - Halting State
C.J. Cherryh - Downbelow Station
Larry Niven - Ringworld, Protector
Larry Niven and Jerry Pournelle - The Mote in God's Eye

There are some books I'm not sure I fully consider science fiction and so hesitate to recommend in this context - like Connie Willis' "To Say Nothing of the Dog" (even "Doomsday" felt a bit of a stretch) or "Hitchhikers Guide to Galaxy" or China Mieville's "The City & The City." And there's a couple books that would have been on here, but their authors' views on some social and political matters make them impossible to recommend.

Some favourites of mine in no particular order:

The Peace War and Marooned in Realtime by Vernor Vinge (available together as "Across Realtime") and anything else by him tbh. They are about a technology that can freeze an area of space in time and the uses it is put to. In the first book it is used mostly as a weapon. In the second, the only remnants of humanity are a handful of people who were frozen in time and wake up to find the rest of humanity gone. They are from societies with different levels of technology, but the book is kind of a murder mystery as well.

The Expanse series by James S. A. Corey. I really like the portrayal of the colonisation of the solar system in this series, and how it splits humanity into different groups. When a technology from an extinct alien civilisation opens a portal to thousands of other solar systems it kicks off a series of conflicts, and the crew of an independent warship, made up of members of the different factions, are central to restoring peace.

Station Eleven by Emily St. John Mandel. It's about a post-apocalyptic world but with an emphasis on how people try to preserve culture, particularly a group of actors and musicians who travel around performing Shakespeare and classical music. It's a really interesting take. It's barely science-fiction I guess but I really liked it.

The Dispossessed by Ursula K. Le Guin. It's about a physicist from an anarchist moon who visits the planet of his origins, where capitalist and authoritarian communist sociopolitical systems dominate, in order to complete and share the theories he has been working on. It's a really interesting depiction of an anarchist society, and its benefits and flaws.

The Murderbot series by Martha Wells. Really fun series about a security cyborg who breaks its programming so that it can do whatever it wants. It mostly just wants to watch TV undisturbed, but ends up being dragged into various murdery adventures. Probably one of the most relatable and charming protagonists I've ever encountered.

Roadside Picnic by Boris & Arkady Strugatsky. This one's about an alien visitation that has left contaminated "zones" at several sites around the world where alien technologies are left scattered around. People called "stalkers" make a living retrieving technology from the zones but they and their loved ones end up mutilated as a result.

Stories of Your Life and Others by Ted Chiang - it's a short story collection but they are really good. The movie "Arrival" was based on one of them.

Red Rising - Pierce Brown
Reminds me I need to reread the series before the next book drops in a couple months.

I enjoyed Project Hail Mary by Andy Weir, it's a really fun and engaging read and Weir always manages to come up with Sci Fi scenarios that feel grounded in reality.

Dune.

I got immersed in the world and realized how influential Dune has been on Sci Fi.

Code of the Lifemaker by James P. Hogan. It was my first introduction to the concept of machine life, which turned out to be quite a formative concept for me going forward. A pity that Hogan eventually went off the deep end, his early books were pretty sciencey before he wandered off into loontown.

Perdido Street Station by China Miéville. Any of the Bas Lag books, really. Incredible world-building completely pulls you in. You feel like you are there, that you know this world. Incredible stuff.

Vorkosigan Saga by Lois McMaster Bujold, with Barrayar as my absolute favourite book in the series. I love the mix of historical with scifi and the way it explores issues of reproduction and disability while having very fun, whacky hijinks.

The Locked Tomb series by Tamsyn Muir!!!!!!!!!!!!!!!!!!

First, as this is my first post here: hi all!

Regarding the topic, in no particular order, they differ so much..

Arthur C. Clark "2001: A Space Odyssey" - a classic, the book with the best movie adaptation ever
Stanislaw Lem "The Invincible" - great book about life and evolution
Neal Stephenson "Snow Crash" - my favorite cyberpunk novel
Arkady and Boris Strugatsky "Roadside Picnic" - the best approach to the issues of extraterrestrial contact

I recently read The Kaiju Preservation Society by John Scalzi. It's a lot of fun, a light and quick read. Basic premise is that a guy gets a job with a charity that looks after "large animals" only to discover the animals are larger than expected.

Same as others have said, it's gotta be The Expanse for me. I saw the show before ever reading the books and it quickly became my favorite show of all time. I'm constantly rewatching it. Then I read the books and loved those even more. Amos Burton is my favorite fictional character from any series. My Elder Scrolls Online character is a Breton named Amos Breton.