Architecture and design
Cohesion and coherence: the architectural and design choices made in a game can't be random. There must be cohesion and coherence to convey a chosen theme. The plot, the mechanics, the environment, all have to convey a message that the player is able to understand without having to guess what the developers wanted. Games can be creative and not follow certain patterns such as cars always having four wheels and the human body always having two legs and two arms. There is room to break rules. The problems arise when objects and structures in a game have no recognizable form and function. The player won't know what to do because the common reference for everyone is common sense. Take a scissors for example. It's immediately associated with cutting, not with being a support to hold something or being a key to open a door. There is a threshold between being creative and going nonsense.
Every type of text has to be cohesive and coherent and that applies to any language. The same is true for level design and game design in general. If the player possesses a power that solves a challenge in one scenario but does not help in a very similar scenario, coherence was broken. If a game travels from one environment to another one, completely different, with no ties to its storyline, cohesion was broken.
Every game has to follow the patterns of its own choices and to obey them. If those patterns aren't followed the player is left confused. Alan Wake for example. In this game safe places are well lighted and the game does obey this rule from start to finish. If trees signal something in a game they should always signal the same thing. If first aid boxes are white, it won't make sense to place a trap in a white box. If red light is a sign of danger, then having another red light, even if it's of a different type, to signal something that isn't dangerous confuses the player.
Speaking about level design, the game has to be cohesive in regards to its theme of choice. That means that levels can't be randomly made. They must be tied to the plot and must convey a sense of progression, both story-wise as well as level-wise. In a city with distinct districts where each one has its own distinctive culture. The architecture, characters and history of each district should be cohesive to reflect the fact that they are distinct from each other. If a player obtains new powers and vehicles during their progress, each level has to reflect that progress by providing opportunities to use the newly attained powers and vehicles. In addition, the levels in the whole game have to have cohesion to convey a story. If many levels take place inside the same building, each level could represent a different building's facility such as power generators, car parking, gym, etc. On the other hand, to mix burning areas with flooded areas, construction sites and a police academy all in one building makes each area feels detached from the rest. Cohesion is lost in this case.
Challenges and obstacles: the challenges and obstacles in the game, from an architects viewpoint, also have to be coherent and cohesive. High cost or overcomplicated solutions to simple problems are illogical. It doesn't make much sense to allow the player to destroy a bridge that is the only available path to complete some objective. If a building has walls made of rock and there is a window made of glass, it'll be incoherent to enter the building by destroying the wall while the glass is indestructible.
In regards to telling stories and conveying an atmosphere, the obstacles and challenges must be part of the environment and the story. As such, a mission to free prisoners from a prison must take place in a level that has challenges and obstacles that make sense in that context. The environment must feel like a prison and the mission should feel as an escape from a prison mission. If the player is escaping from a building on fire, routes through the fire should have been predicted and the player should be able to see it in the middle of the chaos, fire, crashing walls and crumbling ceiling.
Exploration: another important aspect is exploring the environment. Allowing the player to explore makes the player feels attached to the story and engages the player to find out more about it. It's important to note that size alone isn't what tells whether the environment is more or less open to exploration. Wide open spaces with little to discover lack exploration, whereas a small indoor space with many interactive objects invites the player to know more about it.
In most scenarios to explore the environment isn't at top level priority to complete the game, unless an objective explicitly tells the player to find a hidden path or objective.
Collision: all games have to deal with geometry's collision. In the real world if your body hits a step of 1 cm you trip, lose balance or nothing happens. This happens because in the real world your body adjusts naturally to small points of contact and height variations. To simulate the same behaviour in a game requires a huge amount of computing power to do all the required physics calculations. Due to how heavy these calculations are games rely on simplified physics. That's why games have invisible walls or geometry isn't quite realistic at times. For example: for a character to hold some object in their hands and the fingers perfectly close around the object costs a lot of computing power to do it properly. That's why multiplayer levels have smooth and straight walls, with no steps or deep height variations. It's done without "teeths", "zig zag" or protuberances to avoid creating collisions problems for the players.
Invisible walls can, sometimes, be placed to smooth out irregular surfaces. However, they create another problem which is undesired collision problems. In games which require precise aiming there can't be invisible walls blocking the player's fire. Geometry in such cases must have exact per triangle collision. That's why invisible walls can't be placed anywhere except in specific cases, such as floors or places that the player can't be on the other side. If there is a cylindrical pillar and its collision doesn't perfectly matches it, there ought to be problems with collision of weapon's fire. If a game relies on high and low triangle meshes for performance reasons, collision must not be overlooked.
Distinguishable architecture: we have a double edged sword here. If the whole level obeys to a rigid pattern that is to follow the same architecture everywhere we are relying on visual cues to keep things consistent, cohesive. However, abuse of that has the unwanted effect of making the player feel lost because everything looks the same. Why do people get lost inside mazes? Because every wall looks the same. There are no landmarks, colors, textures or geometry to guide the player. Suppose that we have a building where all corridors from all floors look the same. In addition, the whole building is symmetrical and has two opposite sections that are mirrored. Same stairs, same elevators, same corridors, windows, doors. In real life hotels are built with a certain style and architecture that keeps the whole building and surroundings consistent with one idea or a group of ideas. In games, however, doing that can be harmful to the player's experience.
Do you know a good example from real life? Parking lots. How many times people from all around the world, everyday, don't remember where they parked their cars hours ago? Parking lots of supermarkets and malls are large spaces which are usually symmetrical and lack any visual clues to distinguish one area from another. One of the techniques that managers of those spaces employ is to color code or use codes with letters and numbers to help people locate themselves. The thing is, how often does people forget the code for the location where they have parked before? If you want to go to a certain place in a city, what it's easier: memorize the alphanumeric code, the route or some distinctive feature of whatever place you are going to?
I may have mixed up memory, cognition and architecture and stretched it a bit. How often in the world, someone confuses his own car with that of somebody else because they are the same model, same color and/or parked close to each other? This must happen everyday all around the world.