I've recently been reading a lot of science fiction. Most won't be original to fans of the genre, but some people might be looking for suggestions, so in lieu of full blown reviews here's super brief ratings on all of them. I might keep this updated over time, if so new books will go to the top.

A deepness in the sky (Verner Vinge)

scifiosity: 10/10
readability: 8/10
recommended: 10/10

A deepness in the sky excels in its depiction of a spacefaring civilisation using no technologies we know to be impossible, a truly alien civilisation, and it's brilliant treatment of translation and culture.

A fire upon the deep (Verner Vinge)

scifiosity: 8/10
readability: 9/10
recommended: 9/10

In a fire upon the deep, Vinge allows impossible technologies and essentially goes for a slightly more fantasy theme. But his depiction of alien civilisation remains unsurpassed.

Across Realtime (Verner Vinge)

scifiosity: 8/10
readability: 8/10
recommended: 5/10

This collection of two books imagines a single exotic technology, and explores how it could be used, whilst building a classic thriller into the plot. It's fine enough, but just doesn't have the same depth or insight as his other works.

Children of Time (Adrian Tchaikovsky)

scifiosity: 7/10
readability: 5/10
recommended: 5/10

Children of Time was recommended as the sort of thing you'd like if you enjoyed a deepness in the sky. Personally I found it a bit silly - I think because Tchaikovsky had some plot points he wanted to get to and was making up justifications for them, rather than deeply thinking about the consequences of his various assumptions.

The Martian (Andy Weir)

scifiosity: 10/10
readability: 8/10
recommended: 9/10

This is hard sci-fi on steroids. Using only known or in development technologies, how could an astranaut survive stranded on Mars. It's an enjoyable read, and you'll learn a lot about science, but the characters sometimes feel one dimensional.

Project Hail Mary (Andy Weir)

scifiosity: 8/10
readability: 8/10
recommended: 7/10

This is more speculative sci-fi than the martian, but still contains plenty of hard science^[1]. It focuses more on plot, but that's not really Weir's forte and the sciencey bits suffer as a result. Still enjoyable though.

Seveneves (Neil Stephenson)

scifiosity: 8/10
readability: 8/10
recommended: 7/10

This is really two books. The first is a hard sci-fi, how do we build things rapidly in space using current technology. The second half is... kinda wierd, but still enjoyable. Stephenson is less good at the science than Weir, but better at plot, if a bit idiosyncratic^[2].

Cryptonomicon (Neil Stephenson)

scifiosity: 9/10
readability: 7/10
recommended: 8/10

I was recommended this as a book that would incidentally teach you a lot about cryptography. That must have been targeted to complete newbies because I didn't learn much I didn't know already. Still it was enjoyable, if somewhat weird.

The Three-Body Problem (Cixin Liu)

scifiosity: 4/10
readability: 6/10
recommended: 5/10

This started off really well, but then got steadily sillier as the book progressed. I loved the depictions of descent into madness, the surrealism of the 3 body game, and the glimpses into Chinese culture as seen by Chinese. But the attempts to science-bullshit explanations at the end kind of ruined it for me.

Machineries of Empire (Yoon Ha Lee)

scifiosity: 4/10
readability: 8/10
recommended: 8/10

I would classify this more as science fantasy than fiction, since the calendrical mechanics seem to be made up according to whatever the plot needs, but it's a brilliantly written series I thoroughly enjoyed, if a bit difficult to follow at times.

Stories of Your Life + Exhalation (Ted Chiang)

scifiosity: 10/10
readability: 10/10
recommended: 10/10

These are both collections of short stories by Ted Chiang. All are great, but some are incredible. Chiang is an absolutely brilliant short story writer, and I could read his stuff all day.^[3]

The Clan of The Cave Bear + The Valley Of Horses (Jean M. Auel)

scifiosity: 7/10
readability: 9/10
recommended: 6/10

Auel does well at imagining an extremely alien, yet still human, culture, and vividly depicting a prehistorical world. It loses points on scientific accuracy, silly psuedoscience, and her strange obsession with the size of Jondalar's penis. The first book is better than its sequel.

Startide Rising^[4] (David Brin)

scifiosity: 5/10
readability: 9/10
recommended: 7/10

This is a really great read set in a fun universe, but it doesn't actually have much in the way of interesting concepts . Far more science fantasy than science fiction.

Oryx and Crake (Margeret Atwood)

scifiosity: 8/10
readability: 8/10
recommended: 7/10

This is a book which is kind of silly, but perfectly prepared to own it. I enjoyed its deliberately cavalier depiction of a world that's both far more advanced than our own, but also falling to pieces through sheer apathy.

All the birds in the Sky (Charlie Jane Anders)

scifiosity: 2/10
readability: 9/10
recommended: 8/10

This is an even sillier book depicting a world that's falling apart, and with a far sillier plot. Yet for all that it remains a beautiful story, well worth reading.

Ender's Game (Orson Scott Card)

scifiosity: 8/10
readability: 8/10
recommended: 7/10

An enjoyable exploration of childhood genius and ruthlessness.

Hyperion + The Fall Of Hyperion (Dan Simmons)

scifiosity: 5/10
readability: 8/10
recommended: 10/10

Again, this is far more science fantasy than science fiction, but is an incredible literary work. Simmons masters the ability to write in multiple genres and voices within the framework of one cohesive story.

Down and Out In the Magic Kingdom (Cory Doctorow)

scifiosity: 8/10
readability: 8/10
recommended: 5/10

This does fairly well at exploring meaning and purpose in a post scarcity, post mortality world. It's also well written and consistent. But for some reason I just feel meh about it.

Barrayar (Lois McMaster Bujold)

scifiosity: 2/10
readability: 8/10
recommended: 7/10

This is really just a classic court intrigue/civil war novel which just happens to be set on a distant planet with somewhat Victorian cultural norms. But it's a good one. I haven't read any other books in the series, and probably should have read them in chronological order.

Permutation City (Greg Egan)

scifiosity: 10/10
readability: 4/10
recommended: 8/10

To be blunt, Egan is not a great author, and this book is mostly his excuse to elucidate some ideas in philosophy. He gets much of it wrong, but enough of it right that it's worth reading if you're interested in that sort of thing.

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Although I'm pretty sure astrophages violate the second law of thermodynamics.
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See my analysis of one of the book's major plot points here. Essentially spoiler free.
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In particular one of the things that Chiang does really well is take some conceit and explore how people would react to it. What would it be like if the cosmology of the bible was actually real? What about if the world was clearly created 6000 years ago? How about if God, heaven, hell, and angels were all well understood and regularly impacted our lives?
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I mistakenly started with this book, which is the second in the Uplift series, but you'll probably want to start with Sundiver.