Nice read

Random items, not so random lol...

Mouse+WASD keys for 3D first-person movement
This is so much the best way to move a first-person avatar in a 3D space that, until we get virtual reality gear that really works, there is no reason to consider anything else. Dual-joystick setups on controllers can’t match it for precision. First use: unknown.

Independent movement and aiming
Early games restricted the avatar to shooting in the direction that it was facing—as in Asteroids, for example. Separating movement from aiming requires a second joystick, which substantially increases the physical coordination required of the player, but offers more freedom for both player and designer. Probable first use: Robotron: 2084 coin-op, 1982.

Multiple difficulty levels
Designer John Harris has observed that older games, especially coin-ops, were intended to measure the player’s skill, while the newer approach is to provide the player with an experience regardless of his skill level. The old-fashioned school of thought is that the player is the designer’s opponent; the new school is that the player is your audience. By offering multiple difficulty levels, we make games available to larger audiences, which also includes handicapped players. First use: unknown.

Mod support
Modding is a form of gameplay; it’s creative play with the meta-game. The earliest games weren’t just moddable, they were open-source, since their source code was printed in magazines like Creative Computing. When we began to sell computer games, their code naturally became a trade secret. Opening commercial games up to modding was a brilliant move, as it extended the demand for a game engine far beyond what it would have been if players were limited to the content that came in the box. Best-known early example: Doom, 1993."