You think about a Mix of Thief and dishonored, i guess? Least Puzzle, more Sandbox stealth but Open for the Player to approach the Situation (and Not so much Tool/scenario Drive Like the Hitman Games). I would add Safe zones/Houses as in Nobody finds you there. So you can avoid running away from every enemy on the Map, which offen Happens If you have to flee. This could add some kind of inbetween restock or Adaptation options etc. Think espionage Thrillers and so in.

...Also Goddamn how is ot that no one has managed to make something like Theif again outside of Gloomwood (which is admittedly rad as hell?) I only managed to play Theif recently and it's still one of the best stealth games ever. Modern games need to learn how to leave the player alone for a while and let them cook.

Is it weird that I think of Halo 3: ODST as one of the real detective games? Not because it's particularly dedicated to being that, but because the default ending of the game is that you don't solve the mystery and leave unsatisfied. You're just some grunt and what's actually going on is above your paygrade. Learning the truth is a bit of a pain in this ass but it's also basically half of the game's story. I think it was a really ballsy move for what it's worth.