So many suggestions possible with that prompt.
I might suggest the Vlad Taltos series, starting with Jhereg, by Steven Brust. Reaslistic characters, snappy dialog, interesting premise of human’s status in the society, and a pretty far-out series of villains. It comes down to more or less a first person assassin- / intrigue-based plot with cleverly set-up who-dunnit elements here and there, and an overarching storyline, and a good sense of the universe.
Some good suggestions in this thread. If you want even more options - I have been tapping into this Slashdot thread for a decade now, and it’s still giving me winners - which might not work for you, mind (e.g .“Little, Big” by Crowley, it led me to “To Reign in Hell” also by Brust, “Jack of Shadows” by Zelazny,)
Going back to the 80s here, but I would recommend the Taltos series by Steven Brust. It’s a very catchy read, great world-building. It starts as pretty much hard-boiled hitman whodunit in a fantasy setting, but escalated to much higher stakes. He’s still writing the series.
Brusts other stuff is good too.
I second the other suggestion in this thread of Becky Chambers’, classy stuff that really draws you in, very cozy, but not epic sci fi!
The other series I’d recommended then is an old one by Greg Bear: The Way series, starting with Eon. It is about an asteroid which appears in orbit when Earth is at the brink of war, and is one of the most mind-bending, far-fetched sci-fi stories I’ve read, that is still arguably hard sci-fi.