So, pop quiz: What's the number one issue with all those other mystery games?
A: It's the fact once you've solved it, there's no more mystery to it. You forever know who did it.

This game, however, is one of the only games I've seen that solves that issue.
Shadows of Doubt is procedurally-generated film noir, so the dark gritty city will be different for each player.
And... the cases/mysteries, too, are continuously Randomly Generated!

The game literally picks an NPC at times (of the dozens that are generated in your city), and will make them a murderer and has them kill another.
As a private investigator, you will have to figure it out each time. No guides, no YT videos, no forum will have the ability to tell you who did it, as it will always be different.
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That said, your character is not a cop.
You aren't allowed to just walk into a crime scene. You'll have to use your head to think of ways to sneak in and investigate. You'll need to find clever ways to figure out whose prints it is, or what their connection to the victim was, or calculate the trajectory of the sniper round that the victim died to, etc.
Figuring it out, and submitting the paperwork to the authorities, who will make the full arrest and reward you (if you're correct).

The cases are surprisingly tricky to solve. Some leads are dead ends, some will go cold, you will always be looking for your next hot clue, waiting for the serial killer to slip up on their next victim.
The game gives you a virtual corkboard for each case, allowing you to have a "string theory on a corkboard", which you WILL need to solve mysteries. Anything can be pinned, allowing you refer back to it at any time.

Besides murder cases, you can also earn cash and prestige on the side by solving minor cases, such as helping the cops to locate and arrest a wanted criminal. Or investigating someone's cheating spouse, and learn who their lover is. Or helping someone to find a lost ring. And so on.

The city is alive and always moving, the NPCs have simulated lives that are independent of the player.
In the end, your goal is to earn both enough money and enough "social credit" in this corporation-owned dystopia to earn the right to retire in a beautiful community.
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How tough is this game?
Let me put it to you this way: As of this review, I have 27 hours in this game.... and I've only solved 3 murders, and 1 minor case (which was literally just "throw a pie in this one guy's face to humiliate him") in all that time.
(And 2 of those murders were a fluke that my paranoid hunches paid off on. I had very little evidence, and just was suspicious of the NPC. Yeah, I somehow eventually solved two cases through actual IRL instincts.)

This game is Early Access, so be advised of that if you're worried about those.
However, these developers are very active in updates and fixes for this game. (In fact the "sniper murder" cases were just recently added to the game)
At the rate they're going, this game is shaping up to be a solid contender, a real sneaky good game.

So, yes, I do recommend it.