FUNDAMENTALS OF GAME DESIGN, SECOND EDITION

Interaction Model

The most commonly used interaction model for action games is the avatar, found in everything from the original Space Invaders to Half-Life 2. In games that involve exploration or defeating enemy attackers, it makes the most sense for the player to project his will into the game world at a single point, the location of the avatar. However, in subgenres in which the player neither fights nor explores, the avatar
model makes less sense. Tetris, for example, uses a puzzle-manipulation model. Lemmings uses an omnipresent model; the player may click any lemming at any time.

The nature of the actions you choose to include will tend to dictate your interac­tion model. Ask yourself what the player is going to do, and that will tell you how she should do it.