Progression is an important part of a game's design and its purpose is to keep people motivated to continue playing. Each genre handles progression differently, for example beating a map in a strategy game or achieving positive growth in a city builder. There are two categories of progression: player based and game based. Player based is the player improving at the title while game based is the designer providing hooks to keep the player invested. For this post, we're going to ignore player based as I want to focus on the ways designers can keep someone playing.
With every genre, there are different ways that designers can keep people playing and it would be too long to list every mechanic. Instead we can break them down into three categories based on how often they occur.
Short Term Mechanics:
Short Term Mechanics are events designed to occur constantly. Usually every few seconds to a minute and happen so fast that most often the player doesn't even have time to process each individual event. Getting experience and money in a RPG or fighting a wave of "fodder" enemies in an action game are examples of this.
There are two purposes for these events to happen. First is that they act as a basic motivator to the player and show them that they are making some progress within the game. While each individual event may go unnoticed by the player, due to the rate they occur, the player will see a steady rate of growth with the mechanic over time. The second use is that they act as gateways to the next form of progression: midterm mechanics.
Mid Term Mechanics:
Midterm mechanics are those that the player expects to happen over the course of one session. The term "session" is relative to the specific game and can be different based on the genre. For example, playing an action game, a session could be until the end of the level, a hard to reach checkpoint, or about 20 minutes. While in an MMO it could be sitting in front of the computer for several hours of normal play, finishing a quest chain, PvP content or doing a raid event.
Mid term mechanics have a sense of permanence to the world depending on what the mechanic is. For example: leveling up in a RPG, beating a level, unlocking a new power and so on. The important point is that unlike a short term mechanic, the player will remember and look forward to a midterm mechanic.
As with short term mechanics, one reason to have midterm mechanics is that it is part of the process for the final type: long term mechanics. Most gamers base their play-time and accomplishments on achieving midterm goals due to the rate that they are unlocked and their importance to the gameplay.
Long Term Mechanics:
Lastly are long term mechanics, which are mechanics or goals that will happen over the course of several play sessions. These mechanics are in a sense, an extension of mid term mechanics as the player will have to complete multiple midterm mechanics to complete a long term mechanic. Some examples are: reaching max level in a MMO, beating a single-player game, completing a multi-part achievement and achieving a post game goal.
Long term mechanics are important for completing a game, or as a personal goal for the player to achieve. Since long term mechanics are an extension of midterm mechanics, most players will not be thinking about long term mechanics until the end of the game or after completing several midterm mechanics. There is an exception for hardcore gamers who could play the game in the most optimized fashion to get through the game the fastest way possible.
The Balancing Act of Progression:
There are several important points that need to be balance when dealing with progression, some unique to each category and one for all three.
For short term mechanics even though the player will experience them the most, you can't base the entire game off of them. The reason is that mechanics of this type are like candy. They may taste good, but no one can eat candy all the time, as they'll eventually get tired of it. The interaction of short term mechanics is too insignificant to hold the player's attention without having something to build to.
A pitfall some designers fall into is trying to extend the duration of short term mechanics to make them more meaningful. Such as overwhelming players with equipment choices in shops or increasing enemy attributes to prolong fights. Short term mechanics are meant to be quick, a player should not have to spend several minutes organizing an inventory or thumbing through a shop to find what they want. If the designer wants to make a fight between the player and enemy more challenging, give them new abilities but don't make it just a ten minute fight with a fodder enemy.
Another part about extending the duration of short term mechanics has to do with loading screens or clunky UIs. Playing RPGs or strategy titles where the player has to go through multiple menus or systems, these transitions should be as quick as possible. If it takes more than ten seconds to go between menus or access systems which the player will be going through constantly, that time begins to add up and can make the game tedious to play.
With midterm mechanics, the problem with them is that because of the effect they have on the game world, there can only be a limited # of them possible. Eventually the player will reach a point where a midterm mechanic will no longer be applicable such as reaching the max level in a RPG. When that happens, not only does the player lose the progression of the midterm mechanic, but also the short term mechanic that it was attached to.
One workaround is to give short term mechanics ways to effect multiple midterm mechanics. Such as earning experience counting both towards leveling and currency, like in Demon's Souls . Even if the player reaches max level, the act of gaining experience can still be use to purchase items.
Because of the relationship between short and midterm mechanics, if the player can no longer gain anything from a short term mechanic, they may not be motivated enough to continue playing for midterm. For instance, without a short term mechanic to act as progression, the player could play for an hour but may only spend 20 minutes actually progressing in the game. As only the midterm mechanics would be providing any progression to the player.
That same process also applies to the relationship between mid and long term mechanics, but worse as the length of time between the two is far greater compared to short to mid. One of the problems with motivating people with post game content is that by the point that it becomes available, short and midterm mechanics are already used up. Spending hours to get to the point that you may be able to complete an extra hard challenge that may only take a few minutes isn't fun for a lot of people.
Lastly there is one rule that applies to all three groups. In order for a mechanic to be used for progression, regardless of its group, the player must know explicitly how it works and when it takes affect. In other words: randomized events cannot be used as a form of progression. In order to motivate the player they need to know that if they get X amount of gold that something good will happen, or made it past Y to beat a level.
Randomized events due to them not being set have no build up or actions leading to them. However if the player knows that at a specific point, a randomize event is set to happen that would be different. An example would be playing a game where every time at point X, the player would be given a random upgrade which is how the treasure rooms work in The Binding of Isaac.
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Playing Diablo 3, the act of finding loot in the world is not a form of progression because of the randomness of the design. Someone could get lucky and get a piece of gear they need after five minutes of playing, or someone could go 6 or more hours without finding any new upgrades. The act of buying items from the auction house is an example as it has the short term mechanic of collecting gold, coupled with the mid or even long term mechanic of purchasing something off of it.
Continuing with Diablo 3, I'm finding it very hard to stay motivated to play through the end game or known as Inferno difficulty, due to how a lot of the mechanics around progression disappear. Once you reach max level, there is no need for experience (short-term) as the character has unlocked all possible skill upgrades (mid-term). Crafting (mid-term) will not yield anything amazing as the best equipment comes from elite drops. This downplays the need to find gold (short-term) as the best gear will not come from crafting or from the stores (with the exception being the auction house.)
The consequence is that there is only one form of progression left: defeating elites (mid or possibly long term) and bosses (long-term.) But going back to an earlier point, if the player is spending hours playing the game, but only making a few minutes of progress, they're going to get tired of playing.
This kind of problem can also be seen in a lot of MMOs, where the end game just consists of Raid or PvP content with no short or midterm progression. Instead the player will just have to look forward to long term mechanics for their character to show any signs of improving.
DC Universe Online was especially bad in this regard during the time I played after it went Free-To-Play. In order to qualify for end game raids, players had to repeat missions daily to get enough special currency to fully outfit their character with basic end game gear. This gear would be outclassed by what they find in the raids which would require even more grinding to get.
Keeping someone invested through gameplay is a challenge. As more designers look to DLC to keep people going, they need to remember that there is more than one way to progress in a game. No one expects to play a game forever, but if people are getting tired after 30 minutes, then there is a problem.