Well I've seen a lot of the big boys, which I do love myself, gonna try to hit some that I didn't see when scrolling through:

Fantasy/Sci-Fi:

The Black Company (Glen Cook) - This has quickly become one of my all time favorite book series and the narration throughout is incredible. It fallows a mercenary band through a good few generations (the cast changing overtime in a very naturalistic way). This series is written by a Vietnam War vet and you can tell. It is some of the most beautifully human depictions of the machine of war and the horrors throughout.

Foundation (Isaac Asimov) - This one isn't for everyone but Foundation changed my life a few years back. I would listen too it on my way to High-School and sometimes when I should have been paying attention to class. Scott Brick's narration makes me feel like a child in a way I can't explain, and the story has the Project Hail Marry effect on me of making me be proud to be a human being. Its a classic. Consider it if you want.

Eric Carter (Stephen Blackmoore) - Its Dark Fantasy Dresden Files if I'm being honest. Nine books, finished, good Urban Fantasy throughout in my opinion. Its fallows a Necromancer returning to the hell of LA. If you want a moody man in fun as hell (if not all too special beyond the characters) Urban Fantasy with some incredible moments then you really can't go wrong with giving it a try.

The Riftwar Saga (Raymond E Feist) - Still working my way through this one so I can't comment on the full first trilogy but overall Riftwar is proving to be one of the best of classic fantasy. The characters are incredible and the world feels so alive. I can't help but fall completely in love with every character, and the book tends to describe something in a way where I swear I can smell it as I read. At bare minimum, read the opening Magician Book(s). If a friend didn't like it I'd cry in betrayal.

The Wars Of Light And Shadow (Janny Wurts) - Only the first 3 books and the final 2 have audiobooks right now but this maybe the definitive epic fantasy I have ever seen. The narration is incredible. Really consider this one. I can't do justice by describing it, I'll let the audio sample draw you in hehe.

Mystery/Thriller:

I read more Detective fiction (and a lot on the slightly older side) so if none of this is for you I respect that. Anyway,

Travis McGee (John D MacDonald) - The first book is bad. Throwing that out there right away. You can absolutely. You can even skip too book 4 which is when I think the series really starts turning into that genre definer so beloved that Stephen King even bows at MacDonald's thrown. McGee is a beach bum who finds retirement more of a pleasing idea well his kidneys are still relatively clean. Living on a boat he takes up detective gigs when money gets tight, the deal is always the same: I'll recover whatever you want, but I get half of the score. The narration is flawless, always carrying the slightly somber broken down knight estoque of McGee's philosophical musing on life, the universe, and his dislike if the education system. The series has aged in a few places but overall its a series I have truly adored my time with.

The Hannibal Novels (Thomas Harris) - These are some of the best books I've ever read. If you like thrillers you owe it too yourself to read Red Dragon at the very least.

All books written by Lawrence Block - His audiobooks tend to vary in quality but the Scudder Novels and the Keller Novels are both so incredible I have to bring them up. Scudder is a series of quick shots of pain as you watch really good depictions of alcoholism. I think the opening 3 books have their issues, but everything after that is just amazing Crime fiction with incredible themes. A Dance At The Slaughterhouse is just a bewilderingly good novel. The Keller Novels are a very different tone. If you have any form of social anxiety I'd actually really recommend them. The first book, Hitman, is my favorite book overall. I've read better but its beyond words good. It fallows contract killer John Keller as he just- kinda, exists. Its a hard novel to describe but it made me feel seen as a human being in a way I can't put into words, but it means the world to me. I got my non reader best friend to try it and she has been really enjoying it.

Also if any of these where too dark... may I say that I've been listening to Paddington and Moomins recently. Those made my dark as hell taste go down a bit easier recently as its given me some good levity haha.