Help me find a book series like The Witcher or Assassin's Appentice, I need to forget this world right now! Go to town with recommendations!

It's quite old: The Black Company by Glen Cook

He added a midquel, Port of Shadows, in 2018, and there are some really good shorts you can find in his Best of collections that are also recent. I’ve found a lot of folks who read them back when have missed these!

I feel like this is a great rec because The Witcher is pretty grimdark and Cook is a grimdark progenitor. Good pick!

Have you read Discworld? It’s a bit more fun than The Witcher but has similar twists on traditional fantasy and magic ideas

Absolutely not an appropriate recommendation given the details in the request, but a correct one nonetheless.

I have no idea if it’s actually similar, but I googled it and there seems to be an overlap of fans between Farseer and Gentlemen Bastards.

So I’m suggesting The Lies of Locke Lamora! The narrator adds a whole extra layer to the disguises, if you’re into reading by ear

Okay super interesting!
- I should probably describe it: it’s a dark comedy about a group of con artists stealing from the rich in the age of semi-magical science
  
  The 2nd book has pirates!
I could see that, both series really work from very good character writing, if thats someone's thing. I loved both as well.
So I’m suggesting The Lies of Locke Lamora!

Is there some sort of twist that makes it more fun further in? Got halfway through the first Gentleman Bastard and had to give up because I just couldn't care less.

I didn't loathe it like I did with the Kingslayer Chronicle (also DNF), but it's one of a select trio of books that I just couldn't finish, out of some 200 books I've read the post 4 years (Jo Nesbø's "The Bat" being the third).
- If you don’t like it from the start it’s probably not for you, I loved every minute when I read it

old school: Forgotten Realms

More games of thrones-ey, but less so: Wheel of Time

Grand but well paced: Stormlight Archive (Brandon Sanderson)

scifi one-shot: Sea of Rust

Thanks!
I picked up sea of rust on a whim before I was about to board a flight. It was an unexpectedly fun read.

If you want more grimdark and it has to be fantasy, check out Warhammer horror especially the vampire Genevieve. If you’re okay with grimdark science military science fiction, a good chunk of the Warhammer 40k and Horus Heresy lines will fit your bill.

I feel like Hobb is much lighter. For whatever reason I always think of Tad Williams and the Dragonborn Chair as connected to Hobb. I suspect it’s from the Legends anthology but they were only together in Legends II with a different Hobb trilogy setting and Otherland for Williams. Both are great starting points to find authors that have huge bodies of work that could hook you. They were how I found George RR Martin back in the early aughties.

i got one no one seems to have heard of, but its a series by a bunch of writers, and it was stitched together by none other than George RR Martin..

The WildCard series... i just love the different writing styles across the different characters...and its an amazing universe.. i highly recommend it

https://en.wikipedia.org/wiki/Wild_Cards

the short is: alien race f's up a non trivial percent of the human population with a virus.. most die. what neat is the mish-mash of history with a new minority of deformed humans. i think it starts in ~1947 running through the 90s.

British writer Neil Gaiman met with Martin in 1987 and pitched a Wild Cards story about a character who lives in a world of dreams. Martin declined due to Gaiman's lack of prior credits at the time. Gaiman went on to publish his story as The Sandman.

I was aware of the Wild Cards collection as a sidenote in Martin's publishing history, but this is the first time I've seen it recommended by a real person!

Prince of Nothing series would be up your alley I think. Dark fantasy and pretty smartly written.

The Prince of Nothing series.

A very solid series, dense as fuck, with an intriguing way magic works. Just be aware that there can be a fair bit of talking in-between action scenes, there's a lot of time spent in political/religious discourse between characters.

Also, birds with human heads! A prostitute finding out who she slept with by the fact he literally has black cum! Too many scenes of people cleaning themselves up after taking their morning shit!

Got a preference for light or dark?

daaaaark & dreaary
- The First Law trilogy by Joe Abercrombie is your ticket, if you haven't read it already. First book is called The Blade Itself.

Green Bones by Fonda Lee

First book is Jade City. I like that it's set in a 1950's tech world with the magic being only one part of the greater story. Crime, politics, family drama; it's the Godfather with super powers.

To Your Scattered Bodies Go... by Philip Jose Farmer. Everyone who ever lived wakes up on the banks of The River.

If you liked Assassin's Apprentice, Robin Hobb wrote a lot of other excellent books set in the same world.

Empire of the Vampire was great if you want something like The Witcher.

I always liked the Krondor series. It inspired several D&D characters of mine. Like The Witcher, it too has a video game based on it. Though it's from way back in the day on DOS.

You might know this already, but the original series in that universe, The Riftwar Saga, Feist wrote about a DnD campaign he played with his friends. I picked up the first one, Magician, and it felt just like a DnD campaign, so I looked it up and sure enough it was exactly that.

I'm making my way through all of the books and haven't gotten to the Krondor books, so I don't know how different they are as I could clearly see his growth as a writer in just the first series. I'm currently reading through the Daughter of the Empire series that he co-wrote with another author and I'm really enjoying it.

Some slightly off-track suggestions (because genres are a bit misaligned with what you're asking for):

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Gideon the Ninth by Tamsyn Muir (The Locked Tomb series)

Brought up by unfriendly, ossifying nuns, ancient retainers, and countless skeletons, Gideon is ready to abandon a life of servitude and an afterlife as a reanimated corpse. She packs up her sword, her shoes, and her dirty magazines, and prepares to launch her daring escape. But her childhood nemesis won’t set her free without a service.

Harrowhark Nonagesimus, Reverend Daughter of the Ninth House and bone witch extraordinaire, has been summoned into action. The Emperor has invited the heirs to each of his loyal Houses to a deadly trial of wits and skill. If Harrowhark succeeds she will be become an immortal, all-powerful servant of the Resurrection, but no necromancer can ascend without their cavalier. Without Gideon’s sword, Harrow will fail, and the Ninth House will die.

I must admit that Charles Stross' pitch is what got me to pick up the book in the first place, it's just too funny:

“Lesbian necromancers explore a haunted gothic palace in space!” —Charles Stross

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The Final Empire by Brandon Sanderson (Mistborn Trilogy)

OK, maybe not so far off the path ...

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Storm Front by Jim Butcher (Dresden Files series)

The long price quartet

Pale Lights, an ongoing web serial set in the pistols-and-sabres era. The first book's already out for you to read! The author previously wrote A Practical Guide to Evil, which is completely finished.

The Malazan book of the Fallen by Steven Erikson would be my recommendation. Start from Gardens of the Moon and go ahead... It keeps getting better and better!

Prince of Thorns by Mark Lawrence is the first book of a very dark trilogy.

I will also add this, even if it doesn't match the request, but because it's so weird and funny: Shades of Grey by Jasper Fforde. It's about a quite absurd society where people's social status is determined by their ability to perceive colors. And they are not allowed to manufacture spoons. Sci-fiish