I'm playing through a nice little indie game I once picked up in a Fanatical bundle, and it's quite the positive surprise: Intravenous. Also bought its sequel, Intravenous 2, which has even more involved mechanics.
I'd say they qualify as immersive sims. They are certainly inspired by them - the developer openly says so: Thief, Deus Ex, Dishonored, Splinter Cell, etc are major inspirations for the games.
They're top-down stealth action shooters. Think Hotline Miami but with more involved stealth systems.
For the pretty simple indie games that they are, there's a lot of mechanical depth.
You can adjust your walking speed with the mouse wheel, and the sound of your footsteps will adjust accordingly. The surface you're walking on also affects your footsteps' noise level. Pretty much exactly like Thief. Additionally, the equipment you carry can also increase noise level when moving.
Light and darkness also, like Thief, affects enemy detection. In total darkness, enemies can barely see you even in close range, while in the light you're easily spotted. You can turn off lights to create areas of darkness, or shoot them out but that obviously makes noise.
Once you start shooting, pretty much the entire map will go on alert (or, on larger maps, about half the map), because guns are loud. Unless you use silenced pistols, which have a much lower sound range - but still make an audible noise. Walls will block noise somewhat, so shooting someone with a silenced pistol indoors makes it unlikely that anyone outside will hear it.
The AI is also surprisingly good. It will react to everything - you can throw objects to distract them, or even shout something to attract their attention. When you kill an enemy and drag his body away, you leave a trail of blood which patrolling guards will notice and follow. When you leave a door open that's supposed to be closed, guards will investigate. When you turn a light off that's supposed to be on, likewise.
Can recommend.