Dungeons & Dragons is a game in which a single presenter, called the Dungeon Master (DM), describes an imaginary setting to the remaining players, complete with physical features and inhabitants. The players then adopt a mental image of a fictional character that exists inside that setting. The character may act in whatever way the player decides, but the character's limitations are determined by rolling dice that define the character's attributes, capacity for survival, skills and possessions.
Through play, the character, by interacting with the setting as maintained by the DM, seeks to increase their advantage in the setting, and to alter or modify the setting as they are able. This is most commonly done by pursuing "adventures," the end result of which increases the player's possessions, opportunities, skills and hardiness, while causing small but satisfying alterations to the DM's setting.
The setting can be as elaborate as the DM is willing to present; the player's ambition in accumulating power and wealth, or in making a change to the setting, can be as willful as the player wishes. The convergence of the DM's presentation and the player's will produces the effective quality of the game. If the player fails to immerse themselves in the adopted mental image of the character, the DM lacks an enthusiast for which to present the setting. If the DM presents an inflexible, unrealistic setting that acts contrary to the player's will, the player quickly loses the enthusiasm necessary to play.
Game quality, therefore, centers upon finding the correct balance between the DM's motive for producing the setting and the Player's motive for participating in the setting.
That is the Holy Grail.
The setting is usually a mixture of medieval and fantasy, but is not necessarily so. Technology is typically 12th to 15th century European or Asian, lacking gunpowder, global economics or politics. Magic, in the form of spells or physical artifacts, supplants the limitations of the technology.
For those who have never taken the position of the player, the process for creating the character, which identifies the limitations of the character, can be managed as a methodical, repeatable process that becomes familiar, so that the novice will adapt quickly to this part. Interaction with the setting, which consists primarily of communication with the setting's natives, exploration, investigation of clues, confrontations leading to hand-to-hand combat with period weapons, this latter referred to as combat. Combats are the primary cause for potential character death but are not the only cause. Character death enables the player to roll a new character and begin the process from scratch.
For those who have never presented in the position of DM, the procedure is daunting, demanding the retention of considerable information at one's fingertips, the ability to manage players who may stoop to gamesmanship to gain advantage, the creative capacity to imagine, describe and alter the setting as need be, often demanding spur of the moment decisions that may alientate players or soften the setting's capacity to offer the player a meaningful challenge. The DM must often keep much of the information about the setting a complete secret; the preparation of the setting from week to week can be a time-consuming project; and much of the DM's experience separates the DM from receiving empathy from the players, who often see the DM as an adversary. Simultaneously, the DM's power over the setting can induce delusions of grandeur, an obsession with the maintenance and exercise of power, fear of the player's circumventing the DM's plans and a sense of wasted effort spent in preparation for players who fail to appreciate the DM's efforts.
As such, the DM's role is usually the reason that the balance between the setting's motive and the player's enthusiasm tips, causing the gathering of DM and players to scatter, ending the exercise.
The players, too, are sometimes to blame; but not nearly as often as the DM. Bad players in a group are often tempered by good players; but the DM, who stands alone, has no other entity to temper errors in judgement or failings in the effort necessary.
Therefore, if we are to understand how to make the game of a greater quality, we must understand the role of the DM better; to understand what that role is; how that role affects the players; what the players have a right to expect; how to recognize players who are over-indulging in gamesmanship; and ultimately how to locate and maintain that balance that enable consistently good play over a long period.