Cell shaded looks bad.
Use Killer 7 as a reference to it done right.
Don't pull cheap animu shit looks. Do everything as only gradients. No textures except intentional details. Light and shadow to emphasise geometry.
Lots of geometry.
Gradients can also go to the distance, eg bright close, dark away.
Use decals to show changes to environment such as blood.
Ground can be a few as in three shades of brown. Rocks geometry. All gradients. Trees a different shade of brown, bright leaves. Colours don't have to be common. Eg white leaves purple trees.
All is structure. Clean of history, it exists as is. Characters can be complex.
A lot of world. Should be infinate. Characters determinate. All hard set. Things changing your presence. Doing so in hope of satiating that need and avoid further change. Like fire through trees built to burn fast.
All things adult. No exceptions, no allowances. All is complex, denying that is enemy. In self and of others.
Have objects to make alive eg birds chirping, but don't see them. All performance on essential geometry, colour mostly to seperate it isolating differences. Every object is individual that has succeeded in existing. It has no one to thank and it lives for itself. It has already helped you by existing.
Depict what is relevant to what you are doing. Different missions may see different things in the same locations for example. World can be entirely different by what you are looking for, seperate worlds. Enter everything commonly enterable such as buildings. Buildings to occupy space are fine as well. Seperating locations by distance.
Not a lot of wasted time except by choice.
Animations can too be essentials. Can be less complex the more pressing the problem such as pedestrians moving without walking in the distance. Characters not important not existing. Something wrong in seeing things that don't matter. Could be part of a place.
No sky except in colour or gradient matching colour of buildings and landscape.
Edges imposed not essential but if so similar to detail texture. Black. Seperation helps form but wastes attention. Don't detail things that don't matter. Nothing is dirty. lines and shadow point out geometry.
No specular or bump maps. Geometry. Gradients imposed replace specular.
No katanas, samurai or anything else Japanese. World is not a caricature.
Serious, nothing wants to die. Death out of place and showing so, remaining. Done by you or to others. Something remaining to be fixed. Gunplay if any combat. Possibly with casings distinctly left. Combat confined to confrontations, like death it is littering. Danger is not important it can be demonstrated by characters.
Casings show a trail. Gone when followed.
Game not about combat. Not seeming to be about anything. Geometry should look large in all cases. Camera close to ground, looking up by default. Feet of character touching bottom of screen head touching top. Not the top of buildings shown occupy more than the screen.
All impersonal. Things are meant to be seen breifly. The whole scene meant to be seen, already seperated. No need to look at things. individually. Strange stands out but in unopposition does belong.
No environmental sounds. Except while exploring or initial surveying, while decisions haven't been made. When something is urged to do music explaining what is plays. Suiting the character and the land they have chosen or been condemned by. Of having and loss. How eternal longing is a greater truth lived in. Windmill in Killer 7 is a good example. Music different and long. Changing or ending when someone dies. Mission over place is empty without them, frozen in time. Location switch and situation switch. Camera switch eg getting out of a bed.
Change in play. From combat to something else. Previous events distant, from another time and era. A different world that has nothing to do with this one.
World may be different, seen like the last character would now added to a hub in addition to previous ones. Breifly then dissapearing returned to bare essentials.