Been toying around with Intravenous, that was free on gog a couple of days ago, and had a lot of fun.
The gameplay is a mix between a Hotline Miami/any top down shooters and Splinter Cell stealth systems with the noise and stealth meters.
The AI is extremely brutal as once they notice something is wrong (blood, some noise, some door oddly left opened or a room with light turned off..), they'll investigate really seriously instead of quickly giving up, so if you killed a guy and moved it corpse somewhere, the AI will find it by following the unavoidable tracks of blood ( good idea to try to get to melee distance and knock them down from behind to avoid the blood left around due to gunning them down silently) so make sure to check AI patrols to plan your kill spree (considering the amount of enemies on the map i don't think ghosting fully a level is possible out of a couple of levels).
And if something is found (the source of the blood, a corpse, or just you) they'll alert everyone they can and unlike most stealth game, they will not "forget it" once they're trying to find and end you. Sometime the AI will not try to investigate alone and will fetch a couple of its friends to look around too, increasing the difficulty to get rid of them.
But it's still fair because the AI do not seem to magically know where you are, so you can lose your pursuer or observe their hopeless search of you through various rooms.
Because gunfight is very lethal and the AI isn't a SW stormtrooper, getting into a firefight in the open with a bunch of AI at the same time is more likely to end in a quick game over.
Fortunately you can have the usual stealth game tricks : throw an item somewhere to make some noise to distract an AI (be careful that it is not at ear distance of too many of them as your distraction may instead make things harder for you) , you can attract AI with doors intentionally left open, turn off lights or generators, crawl , get into vents , use suppressed pistols etc...
You can bring various gadgets along a rifle and a pistol, usually the more you bring the less stealth you are (there are various body armor that you can get if you want, but each will lower your stealth more or less), seems like for stealth pistol, the MK23 is king as i found the other sometime do not one shot unsuspected enemies for some reason, but when an AI is alerted i noticed they seem to resist 1 more bullet than when they're not.
Shooting a non suppressed pistol is the same as pushing the big alert button, half of the map will converge toward the sound source, so it can be useful in a few cases (if you have a lot of ammo, grenades, mines i guess, though the AI is very accurate in its shots) or making the difficulty utterly greater.
For the story it is very very inspired by Punisher, just your character is named Steve instead of Frank Castle and want to avenge his brother instead of whole family by killing every drug addicts and junkies that were part of it, then their drug ring, then more kingpin , all the while helped by some techy guy that will very likely stab you in the back like in all those Punisher tropes .
But it's well done and the stealth play is very good, but the difficulty is no joke at all in this game even on the lesser difficulty level.