Mark Lawrence's "Book of the Ancestor" and "Book of the Ice" series.

Someone else suggested N.K. Jemisin’s Broken Earth series, which is also an unusual take on the post-apocalyptic and survivalism stuff that a lot of people are into these days.

Stephen King’s Dark Tower series. Mix of cyberpunk post-apocalyptic parallel universes with science so deep it’s magic.

(Trying not to give away too many spoilers!)

As a bonus, there’s an extended reading list which ties the Dark Tower into books and short stories from King’s universe.

I'd have to say China Mieville's Perdido Street Station.

I've been trying to get into the first Gormenghast book and finding it difficult to get into the swing of. Does it get any easier as you go?

Mark Lawrence has several trilogies that fit into this genre. They're fantasy books but the setting/universe is based on science fiction.

Series that I've read and recommend:

Broken Empire

Holy Sister

Red Queens War

I found them all an enjoyable mix of dark/grim fantasy with a good mix of humor. These series all tend to follow an anti-hero or in Broken Empire's case you could argue it's a villain protagonist given just how unsavory a character Jorg is. Even still I found myself liking and rooting for that bastard.

• The City We Became and The Broken Earth series by N.K. Jemisin.
• Light From Uncommon Stars by Ryka Aoki
• Remote Control by Nnedi Okorafor

Honestly, Discworld is both sci-fi and fantasy.

The Broken Earth series is really original and well written.

Wait, Gormenghast has Science fiction? When does that show up? I only read the first book so far and don't remember a lot.

I know this is answer is overdone at this point, but a pretty good chunk of Brandon Sanderson's books are this.

• The Captain by Will Wight
• The Shadows of Dust by Alec Hutson
• Portal to Nova Roma by J.R. Mathews
• Starship's Mage by Glynn Stewart

The Black Ocean series

Halo Forerunner trilogy.