Art Style
One aspect of being a designer, being able to decide which art style would suit the experience better and be suitable for the public.
Main Style
The main style of the game should first be analysed in regard to the target audience. This can vary depending on the intention of the designers, it can push boundaries but the line there is very thin.
Most likely, a cartoon style will suit better a younger audience, since it is easier to interpret and creates a sense of easiness and a lighthearted experience. But it could be too plain or boring for older people.
The art style does have specific cases, like when using nostalgia or keeping an older series feeling through time. A game like pokemon, for instance, cannot become super realistic, it would make the main feeling of the game completely at odds with its intention.
Contrasts
Contrasts are very important inside games. They don't need to be obvious, but contrasts in colour or placement can help in directing the player towards the goal of the game.
Colour contrasts should be part of the same area. If they contrast too much with a completely opposite colour for too long, the player's eyes will get tired very quickly.
Synchronization
All the art inside the game must be synchronized, in other words, they need to talk to each other on the screen.
The styles and colours must feel like they pertain to the same world.
A game that uses primarily soft colours shouldn't suddenly be using strong colours like bright red for no reason. It's fine to mix them in a few key moments, but the colours and textures should match the overall intention. This helps to create a sensation of comfort and make the player get used to the game.
There might be some exceptions, like games that have multiple worlds and therefore multiple types of environments. In this case, the change in colours is naural because there is a clear natural reason for it. However, the textures and style should still maintain the aspect. Even if a game where there is a change from cartoon to realistic might sound like novelty, it is not a good idea in the long run.
Shaders and Textures
Shaders and textures can completely change the feel of a scene. Depending on the lighting and shadows procedure, the scene can have a flat 2D or deep 3D feel to it.
The textures need to follow a designed style as well. Mixing simple textures with complex and intricate ones will only confuse the player.
Even more realistic and complex games should have a scene that is not noisy in their composure, so the shader type should also be defined early.
The shaders and the textures work very intimately together. Some textures don't really match well the shader designed for it. For example, a cel-shaded style of shader works best on simple well defined textures, since the purpose of the cel-shading is to have clearly defined colours. Using an intricate texture will make the effect very difficult to see and create a distracting effect on the scene.
