For me, The Murder of Roger Ackroyd is the best Agatha Christie. Go in blind. For non-Poirot books, Crooked House and Murder at the Vicarage are also top shelf.

If you like Christie, I would also recommend Louise Penny. She's very stylistically and thematically similar. Still Life is a great mystery and also a nice window into a cute pastoral Canadian town.

For something off the wall, Leech by Hiron Ennis. A detective is dispatched to a snowbound manor house to investigate the death of his predecessor. However, the detective is a sentient parasitic leech hivemind and the killer he pursues is an alien fungus body snatcher.

@Hstansss For light mystery, The Thursday Murder Club books are a good read. A group of retirees in a senior living center have a hobby of trying to solve cold cases. The characters are funny and quirky.

I actually wrote a super long post on some of my favorite mystery series of a couple different flavors for another post when I was bored at work the other day.

Dark, more substantial, more explicit

• Karen Rose's Romantic Suspense. The world is full of monsters, and Karen Rose will introduce you to them all. These aren't fantasy monsters, but the human kind. They do fucked up shit and you see a lot of it. WARNING: I think it's all off screen, but this includes children as victims of sexual crime. However, to me she's the gold standard for fiction authors. Her characters are broken, and there's a dichotomy between how they see themselves when they're the character leading a scene and when they're a side character that's really well done. She gets you inside the heads of both the main pair of characters as they heal and fall for each other and the villains, and does an exceptional job at being aware of who knows what and when in their interior monologues. I love the way the books are paced, and the mysteries are complex and layered. I don't really read romance so can't comment on that part, but I really like how the developing partnership builds out the characters. In sharing their deepest darkest secrets with their co-lead in a given book, the characters get really fleshed out. This is hands down my favorite series and I go through it start to finish on audiobook 3-4 times a year since discovering it. You don't need to read the entire series from the start, but they're broken down into sub-series by city, and those sub-series have strong arcs through them. So far example, you would want to start the 3 part Sacramento series with Say You're Sorry and go in order. This is probably not "first read" material, but I can't give a list of my favorite fiction and not pitch what I think is the best I've read. There's really nothing else like it. If Game of Thrones isn't too much, this is probably OK.

Victorian Era

• Lady Sherlock by Sherry Thomas. This is a wildly popular setting because of Sherlock Holmes, and I don't think most manage it very well, but when you do nail the setting, it really creates a deep feeling world. Holmes adaptations themselves are also relatively popular, but this is the most interesting one to me. Charlotte Holmes is thrown out of her house for refusing to fit in to the era's norms, and invents the Sherlock character we all know and love to survive and use her brain. Of all the adaptations, this is the one that feels like the same character deep down to me. It also highlights the issues with the era instead of romanticizing them like most, without being overbearing. You don't have to read in order, but book one sets up the premise.
• Glass and Steele by CJ Archer. This one is an awesome mesh of different settings and genres blended really well together. It's Wild West outlaws coming to Victorian era England for a fantasy epic styled coming into the light of magic, where magicians who have hidden themselves for fear of prosecution from the craft guilds come into the light. The mysteries don't ignore the magic elements, but don't use them as a crutch and stay broadly true to the era, and the take on magic is unique and interesting. You really want to read this from book 1.

-second post because I wrote way too much

One series I got into for a while was skull duggery pleasant. Very dick Tracey vibes from the main detective, but the catch is he is an animated skeleton who investigates mysteries in the world of magic and has a teenage girl that tags along as his apprentice. All in all a fun read that stays in the detective noir vein but also takes a couple steps into the fantasy realm.

Short thriller/comedy/sci-fi that I really liked was The Murderbot Diaries series by Martha Wells

I'm not sure they really fit into the category of murder mystery that you're looking for, but I recently read both The Seven Deaths if Evelyn Harcastle and The Devil and the Dark Water and absolutely loved both of them.

Henning Mankell's Wallander books are great, if you're into the slightly depressing Nordic vibe.

The book that got me back into reading for pleasure after many years of not doing so was a comic called Whiteout by writer Greg Rucka and artist Steve Lieber. It's a murder mystery set on an Antarctic research station.

I would also suggest pretty much anything written by Ed Brubaker and Sean Phillips published by Image. Some of the best noir (in any format) you will ever read is by them. I particularly enjoyed

• The Fade Out - a Holywood scriptwriter in the 1950 wakes up in a bathtub after a party he can't remember in a house he doesn't know, and discovers the starlet of the film he's currently working on dead on the sofa. It's fair to say the ending is a little weak but getting there is quite a ride
• Fatale - a Cthulhu/noir about a femme fatale and her trials and tribulations over a century or so
• Incognito - a superhero/noir about a supper villain in witness protection who tries to g et back into the world of supers, this time as a hero. But of course no-one trusts him on either side

I was also disappointed in the Silent Patient!
I like the Jimmy Perez series by Ann Cleeves set in the Shetland Islands. The descriptions of the scenery alone are worthwhile.

Highly recommend Raymond Chandler’s books. He’s one of the reasons I got so into reading.

Some other good books are by Rodica Ojog Brasoveanu and George Arion, but sadly I don’t think they’re translated to English.

I have really enjoyed Japanese honkaku mysteries. They're based on the classic British mysteries of the 1930s. Not many are translated but I liked The Honjin Murders and The Tattoo Murder Case. Search honkaku and read them for the Japanese take on the country house murder.

Everyone in my Family has Killed Someone was a very fun read for me! Family drama in an Australian ski resort told after the fact in 1st person.