Dark Sci Fi books?

I Have No Mouth and I Must Scream by Harlan Ellison is pretty bleak. And it’s a short story as well so it wouldn’t take much time to read.

Any SF by Iain M. Banks has its dark moments.
A lot of Stephen Baxter’s work is quite bleak.
George R. R. Martin’s short stories are quite grim
Kristine Kathryn Rusch’s novels can be quite heartbreaking, especially those that aren’t part of a series.

Oh, yes.

Warhammer 40k.....

It is pretty much as dark as it gets.
They now even have a "Crime" and "Horror" range.
As I said, the books by Abnett are awesome. If you start, start with Eisenhorn Xenos and work your way through the sequels. They are now also available as cheaper ebook bundles.
And there is of course the amazing "Night Lords" trilogy, which follows a warband of monstrous villains and one that impressed me so much I have spend a lot of time and money collecting and painting a Night Lord army. The story of the once noble Talos Valcoran, who still has a tiny shred of honour, and his psychotic squad, told through the eyes of their enslaved human servants is a fantastic feat of character-development and world building. I love it.

Oh, you were talking about "real" books, were you.....
sorry....

I've read 1984 and The Road, I'll look up Flowers for Algernon though.

The Road was very good, I read it very quickly, recently watched the film which was also very good, utterly heartbreaking, had me in tears at the end.

I read 1984 when I was a teenager but funnily enough never read Animal Farm, I missed a lot of secondary school due to mental health struggles, I've also got Lord of the Flies on my to read list, along with a few others I missed out on.

Indeed! I'd seen the movie a number of years before I read the book, but both were just outstanding.

Beth Chalmers also narrates some of them. (I plan to buy them after I’ve made a dent in my BF backlog. I like her work, especially Raine & Veklin).

I’ve only read 1 book in the Horus Heresy series, (we randomly got it from a used bookstore) The Flight of the Eisenstein: The Horus Heresy book 4  (James Swallow) and it’s really good. The plot was not difficult to comprehend, the imagery & world building vivid, & the characters,( especially the lead character) were compelling, I thought.

tuigirl does very helpful & enthusiastic wall of text. I don’t mind. 😁⭐️ I hope your internet troubles have been resolved tuigirl. I read in another thread it takes some effort to even just post in this forum. 👍🏻

Flowers For Algernon is superb, one of the books of the century, IMNSHO.

An interesting side fact about it is that after it was adapted into the film Charly (1968, which won Cliff Robertson a Best Actor Oscar), there were plans to adapt it into a musical, starring Michael Crawford. They went as far as having songs written for it. After the plans folded, the songwriters managed to repurpose one and reuse it for another musical. The song was eventually called “Tomorrow” and it was used in Annie.

To go a little more in-depth:
possible entry points:
Ghost Maker (Gaunt’s Ghosts): first part of a 12 book series, pretty much a military focused series, with set dressing like the occasional weird psychic power or giants in power armour. Fleshed out characters, cast of about 5 major characters, 10 secondary but interesting characters and one of the most loathesome characters in any Warhammer, or any ANY really, fiction. It’s focused on humans, during a military campaign to recapture a couple of star systems. 

Xenos (Eisenhorn saga): first of 10 (the tenth to be released) focusing on one of two Inquisitors (people who are effectively above the law, who investigate dangerous Individuals within the Imperium). The worlds are really well established, well drawn, the characters believable annd engagingly written. Dos involve psychic powers, introduces them carefully and introduces other things like Astartes (Space Marines) but does not focus on them. It’s a sort of Mission: Impossible structure. A small team od experts versus equally expert and dangerous people. 

the Horus Heresy: 40 odd books* of varying quality, a vast sweeping epic with dozens of characters in each book, full of betrayal, explosions, death, hope, hopelessness, the death of empires and treason most foul. LOTS of Astartes. LOTS of psychic powers. LOTS OF DEATH. Your favourite character will die unless they’re Bjorn, Cawl or Thiel. You will hate Erebus. Early on in the series, thematically any story around “the dropsite massacre” can act as entry points. Horus Rising, Flight of the Eisenstein, Fulgrim, Legion or A Thousand Sons give a good entry point. As things go along, certain plot lines get their own books whereby you can sort of just follow those characters.
*Fair warning, this is a series that crosses all media, full length novels, short stories, novellas, audio dramas.