Game Goals
Game goals are goals that are built into a game and communicated to a player as objectives that must be met in order to successfully complete or win the game. Some games have goals that must be determined as part of the game (in other words, the first goal is to find out what to do), others have goals that are implicit or understood in the context of the genre (for example most fighting games), while others blatantly expose the objectives (strategy games that state specific winning conditions).
Generally speaking, there are two types of goals. Those that are necessary to complete, finish or succeed at a game, and those that are not. Goals that are required are called Required Goals, while those that are not are called Optional Goals.
Of course, there are times when certain goals arent easily determinable as either required or optional. For example, some games may offer players a wide variety of goals and specify that only a certain number of these must be accomplished. In this case each of those subgoals, taken individually, are debatably both required and optional at the same time. Of course, their actual status depends on what other goals have been accomplished. In the previous example, once the minimum number of goals has been met, the rest of the goals automatically become optional.
Examples
Strong Examples
Shining Force 2
As a tactical RPG, the goal of each battle is to win, and to level up/improve your charicters. Overall, the goal is to kill the evil sorcerer Iom, and save the world from certain doom. This is accomplished in a linear battle fashon, breaking the overall game goal of beating all the battles into beating each unique battle as it comes.
Diablo 2
In Diablo 2 the goal is basically defined by its genre, a dungeon crawler where you must kill hordes of minions in order to reach a high enough level to defeat the main boss in the chapter. There are both optional and required goals in this game, for example you must acquire the Horadric staff to advance in the game, but you do not necessarily have to kill the Countess. The goals are simple, specific, and easy to execute, but take hours of game play and character advancement to fulfill. Almost always the goal is to find a character, find an item, or find and kill a boss.
Super Mario Bros.
Super Mario Bros. is a classic example. The simply defined, required game goal is to make your way to the end of each level by defeating foes and conquering obstacles. Once the castle level is reached at the end of a world, the player must defeat King Koopa and then he/she proceeds to the next world. The game also presents several optional goals such as finding invisible boxes, discovering warp pipes that transport you to new areas and worlds and other goals that are extremely well hidden like the "fireworks secret".
Super Monkey Ball Banana Blitz
The goal of this game is surprisingly straight forward an intuitive. Super Monkey Ball Banana Blitz's gameplay dictates that the player guide his or her monkey through a stage and subsequently through a goal structure in order to recieve credit for completing the stage. There is no other criteria present that also qualifies as a goal in the game.
Shadow of the Colossus
The goal of this game is to defeat all of the Colossus's in an interesting style where every battle is a boss battle. First you must find the Colossus and then you must figure out where its weak points are so you can defeat it. This system where you battle against only one enemy, albeit they are usually huge and very challenging, is fascinating and unlike any goal oreinted game I have ever played.
Gears of War
The campaign mode is comprised of five chapters. In each chapter, the player/s must complete specific tasks, such as: reaching the fuel depot, taking out the berserker, covering the entrance to the mansion, etc. After each goal is achieved, the player/s is prompted via text or in-game audio/visual cues as to what their next goal is.
Sonic the Hedgehog
This game is a good example of game goals. In Sonic the goal is to get through all the levels and ultimately defeat Dr. Robotnik. The player is also given optional goals throughout the game, such as collecting chaos emeralds.
Jet Force Gemini
The main objective of this game is to stop Mizar from taking over the galaxy, and all of the game is revolved around this. All of the small goals, such as rescuing Tribals, an enslaved race of bears, or finding a key to open the next door, is essential for completing the bigger task of defeating Mizar.
Legend of Zelda: Ocarina of Time
The main objective of this game is to defeat Ganondorf/Ganon and save Hyrule and Princess Zelda. Many but not all other goals are devoted to this end. Some examples of necessary subgoals include collecting three Spiritual Stones, collecting six tokens, one from each of the six temples, getting at least two swords, and collecting the necessary keys.
Weak Examples
Second Life
This game is a completely open ended massively muliplayer game where all content and "gameplay" are created by the players. The game itself is more of a giant sandbox for players to create whatever they want and to share it with who ever they want. Some players even made real world financial profit off of their creations.
World of Warcraft
Yes, of course being an MMORPG World of Warcraft is full of quests, and dungeons which are essentially goals put into the game by the design team. However, all of the goals are optional, a player is not "forced" to complete any one goal unless completion of that goal is a prerequisite for the next goal that they desire to complete. In World of Warcraft the freedom to do whatever the player chooses is absolutely apparent, and they pick the goals that they desire to accomplish, though the game may strongly suggest some like leveling up, class based quests, and attunement/keying.
Oblivion - Elder Scrolls IV
This game is made up entirely of optional goals. There is no pressure to complete any of the optional goals and there is actually no pressure to do anything at all. If you don't feel like the usual play you can walk around somewhere and pick plants for making potions and sell them and thats just one of countless things to do that have nothign to do with any storyline at all. You can also sneak around and rob and kill everyone in thier sleep and earn infamy if that's what you feel like doing. You can even customize and create your own spells and enchanted weapons. These reasons are what enhance the game because the gameplay and game goals are based on who ever is playing.
Street Fighter III
As with most fighting games, the only real goal is to knockout your opponent in order to move on to the next one. What is unique about SF III is that you get points for landing hits, using special/super moves, using counterattacks, chaining together attacks (combos), and parrying attacks. Obtaining a high score is not a set goal however. It is up to the player to decide whether they want to get a lot of points or just beat the opponent any way possible. The point system is merely a gauge of how well you perform (like bragging rights).
Legend of Zelda: Ocarina of Time
Some examples of optional goals from this game include getting four bottles, collecting 100 Gold Skulltula tokens, and collecting all the Heart Pieces. These all are examples of weak goals that, though not required, are part of exhausting the game.