The human brain loves looking for ways to optimize. One of the joys of playing games is exploring the decision space and finding ways to improve your strategy. Once an optimal strategy is found, however, the brain will stop being stimulated by a problem and become bored. The ideal target for game depth is a steady progression of learning throughout the play experience, so that strategy and optimization are revealed constantly as a player explores, stimulating both the novice and expert brain alike. This article will look at tools to increase game depth and how you can apply them to your own designs.

Opposing Player Psychology


The greatest and most common source of depth is opposing player psychology. The human mind is a wonderfully complex object of study. Evolution has programmed us to be intensely interested in learning how other people think. Thus, putting human psychology at the core of your game is a great way to ensure depth. How do you do this?
1. Counterstrategies- Every strategy in your game should have a counterstrategy that can defeat it. Look at a game as simple as rock, paper scissors. The game rules are trivially easy- each player simultaneously chooses rock, paper, or scissors. Scissors beats paper, Paper beats rock, and Rock beats scissors. Despite this simplicity, there are annual rock paper scissors championships and highly competitive players who play the game for years. The entirety of the game rests in deducing the precise psychological state of your opponent and staying *exactly* one step ahead of them. Whenever I design a game, I always try to incorporate a rock papers scissors element into the high end strategy to ensure long-term depth.  For any strategy you want to enable in your game, make sure there is another that is dominant against it.
2. Hidden, Asymmetrical Information- By selectively giving information out to some players and not others, players will be driven to “read” the information known to their opponents based on their actions. Perhaps the greatest use of hidden information to develop game depth is found in Poker. The mathematical probabilities of a game of poker are relatively straightforward, but the true skill comes in being able to discern what cards each other player holds while concealing your own. This mechanic taps into our deep seated need to learn and predict the behavior of others. Deviating from the mathematically “best” strategy in order to deceive opponents about your game position greatly increases the variety of possible strategies, greatly increasing game depth. Give players access to exclusive information and give them opportunities to make a series of public decisions based on that information to best utilize this tactic.
3. Personal Revelation / Discovery- Games can acquire depth by forcing people to make connections and reveal personal details about themselves and their lives. Unlike the two strategies above, personal revelation taps into a more social (rather than strategic) side of psychology. Party games like Apples to Apples, What Were You Thinking, and Taboo all take advantage of this mechanic. In Apples to Apples (as well as its more profane counterpart Cards against Humanity), one player each round is listed as the “judge” and reveals an attribute card (e.g. Happy). Other players must play noun cards (e.g. Bill Clinton, Rollercoaster, etc.) that they think the judge will most associate with the attribute card. The judge picks the winner and then play rotates to the next player as the judge. Forcing players to get into the head of fellow players triggers this same need to understand others but in a more friendly and social context. Personal Revelation / Discovery mechanics can be added to a game by either
A. Restricting communication channels (e.g. Taboo, Pictionary )
B. Setting goals that hinge on other player preferences/background (e.g. What were you thinking, Apples to Apples)

Time Restricted Decisions


Even relatively simple decisions become deep when they are made under time constraint. Learning a basic attack move in God of War is easy, but applying it successfully to dozens or hundreds of enemies simultaneously is a more engaging challenge. In the pattern matching card game SET, each player must identify sets of 3 cards that do not have any two traits in common. As soon as a player sees a pattern, they yell “Set” and grab the cards off the table, denying others the chance to grab it.
Forcing players to temporally compete against other players, automated obstacles, or a set timer can transform basic mechanics into deep learning experiences as players constantly try to improve on their reaction time and expertise with a skill. When using time restriction to increase depth, be very careful about keeping the decisions themselves relatively simple or you risk players becoming overwhelmed.

Complex Decision Space


The more options there are, the harder it is to figure out the final game resolution. This is the type of complexity that is measured by computer processing power. Increasing the total number of permutations available to players will increase game depth. This can be done easily by increasing the number of rules and mechanics within a game. This, tactic, however, will greatly reduce the elegance of your game, so I do not recommend it. Some other tools to increase decision space include:
1. Probabilistic Outcomes- If every time you reach a certain spot in a video game level, a monster jumps out and attacks, players will quickly learn to avoid that spot. If the monster only probabilistically attacks, it will take far longer for players to realize the strategy. Similarly, games involving dice, a shuffled deck of cards, etc. force players to consider a wide range of possible outcomes when determining the correct strategy.   I cover other strategies for how to manage probability in games here.
2. Exponential Decision Trees- The game of Go has some of the most elegant rules in the history of game design, yet it has more possible game states than chess.  By allowing for a large variety of possible moves on any given turn, planning for future moves becomes more and more difficult, increasing game depth. This can be a dangerous tool as well, however. If moves become too obscure, players will have difficulty connecting their early game decisions to an overarching strategy for victory. This can cause players to lose interest in the game and quit. Thus, with exponential decision trees it becomes even more important to have interim goals and guidelines to give people a feeling of making progress and to help direct players.
Game Depth is often presented as opposing game elegance and simplicity. Clever utilization of the above tools, however, can help ease this dichotomy. Remember that more depth is not always better.  You need to custom tailor the depth of your game to the audience you are trying to reach. Making a deeper version of Chutes and Ladders misses the point of the game.  The best games are “easy to learn, difficult to master” for their target audience.  Know your audience and experiment with your core mechanic to find that critical balance.